About Bill Hartzer, Expert Witness

What this practice is, and what it is not

I am Bill Hartzer. I have worked in digital marketing since 1996, and I am retained by attorneys — plaintiff side and defense side, and frequently as a rebuttal witness — in disputes where the contested facts sit inside advertising platforms, analytics systems, and the records that advertisers, agencies, publishers and vendors generate around them.

The work is narrower than the phrase digital marketing expert suggests, and deliberately so. I am not retained to say whether a campaign was good. That question has no external answer, and an opinion built on it does not survive two minutes of cross-examination. I am retained to establish, from records, what was configured and when, under which login, what a platform charged, what a client was invoiced, what a client was told, and where those four diverge — and then to say what that sequence supports and, just as often, what it does not.

I am not an attorney, and nothing published here is legal advice. My opinions concern records, methods and measurement. Whether conduct was a breach, whether a statement was material, and what a claim is worth are questions for counsel, for the trier of fact, and in damages matters frequently for an economist working alongside me on the part of the model that is not a marketing question at all.

Working in digital marketing since 1996

The practice rests on having been a practitioner first, across most of the periods a litigated record now crosses. Paid search moved from manual keyword bidding to automated bid strategies the advertiser does not directly control. Measurement moved from server log files to JavaScript page tags to server-side collection, where the data is assembled on a machine one party owns and can configure. Social media went from an organic channel to a predominantly paid one. Commerce moved from an owned checkout to marketplaces where the seller does not hold the transaction record at all.

That history matters in litigation for one narrow, practical reason: a record has to be read as of the date it was made. A column labeled Conversions in an export from one year does not necessarily mean what the same column means three years later, because the platform changed what it counted, renamed it, folded modeled figures into it, or shifted the attribution model that fills it. An expert who reads an older export with current assumptions produces a number that is wrong in a way the other side can demonstrate on the record. Knowing what an interface reported at the time is not nostalgia. It is the difference between a reproducible figure and an indefensible one.

The channels this practice covers are the paid ones — search advertising, display and programmatic, paid social, and online advertising generally; the owned and organic ones — social media, email, content and affiliate; commerce and retail, including marketplaces and the conversion behavior of a website; and the measurement layer, meaning analytics, tracking and attribution. The disputes those channels produce are a shorter list: agency and consultant performance, scope, performance-based compensation, click fraud and invalid traffic, affiliate and impression fraud, false and deceptive advertising, trademark use in advertising, and the quantification of claimed loss.

The four assignments counsel actually calls about

Nearly every engagement is one of four things, or a combination of them:

• Reading the record. What a platform export is, what it counted, what it estimated, what it omits, and what a specific field means. Much of the value here is definitional, and definitional error is the single most common defect in the reports I am asked to rebut.
• Reconciliation. Comparing what the platform billed, what the platform’s own reporting says was spent, and what the client was invoiced and told. The comparison is arithmetic, the records are held independently by different parties, and almost nobody performs it during the relationship — which is why it is the recurring finding rather than a clever one.
• Reconstruction. Building a dated, sourced timeline from change history, account ownership and access records, campaign structure at intervals, communications and deliverables — and marking which parts of it are established and which are inference.
• Rebuttal. Examining a report that already exists and identifying where the definitions, the method, the arithmetic or the underlying records do not carry the conclusion. This is a substantial share of the work in this field, and I write about it explicitly, because counsel evaluating a rebuttal engagement rarely finds anything written for that situation.

Where my subject ends and someone else’s begins

Declining adjacent work is part of what makes the rest credible. Search engine optimization as a discipline — ranking causation, algorithm updates, the technical audit of a site’s search performance — and the admissibility questions that surround expert testimony are covered by a separate practice site, and where a matter is squarely about either, it belongs there. Domain names, registrar conduct and cybersquatting sit with a different practice again. Internet matters generally, including online defamation, sit elsewhere still. So does search marketing consulting: this site is litigation only, and the consulting practice is a separate business that takes no part in a matter I am retained on.

Other boundaries are simply outside my competence, and I say so on the first call rather than in a deposition. Forensic attribution of the human being behind an IP address, malware and intrusion analysis, accounting reconstruction beyond the marketing records themselves, survey design for consumer confusion, and econometric damages modeling of the kind an economist builds are all work for someone else. The usual arrangement is that I work alongside an expert in that field and keep my opinions inside the marketing record. An expert whose competence expands to fill whatever the assignment requires is the expert opposing counsel most wants to depose.

What I decline

The list is short and it is worth stating, because each item is a question counsel would otherwise have to ask.

• Fees contingent on outcome. Not in any structure. Compensation is discoverable by rule, and an arrangement that moves with the result is a gift to the other side even where it is permitted.
• Assignments phrased as conclusions. Determine whether the agency overbilled presupposes the answer. Reconcile agency-invoiced spend against platform-recorded spend for a stated period, and characterize any divergence does not.
• Opinions on the ultimate legal question. Whether a duty existed, whether it was breached, and whether a representation was material are not marketing questions.
• Matters where the record no longer exists. Retention windows in this field are short and rolling, and when the decisive data has aged out, sometimes the correct advice is that an expert cannot help. That call is cheaper to make in week one than in month nine.
• Matters where the conflict check does not clear. No exceptions, and no negotiation about it.
• Requests to state a conclusion more firmly than the method produced it. Rule 702 as amended in 2023 makes overstatement an admissibility problem as well as a credibility one, and a marketing method that has been asked to carry more weight than it can is the failure mode in this field.

The standard-of-care question, answered before anyone asks it

In a negligence claim against a service provider, the plaintiff has to show what a reasonably competent practitioner would have done. In a licensed profession, that first element arrives from outside the case — a licensing board, a mandatory body of practice, a credential with disciplinary consequences behind it. Digital marketing has none of that. There is no general licensure requirement, no entry examination, no continuing-education obligation, and no body that can stop anyone from practicing.

Nor is there an agreed set of documents to substitute for one. The advertiser-side trade body, the ANA, publishes a master media planning and buying agreement template and describes it as a starting point for a customized contract, adding that changes to its provisions should be expected. The agency-side trade body, the 4A’s, published guidance on 1 July 2024 stating that it does not recognize ANA templates as industry standards. The Media Rating Council runs genuine annual audits by independent auditors — of measurement services, covering sample design, invalid traffic filtration, controls and disclosure. It audits products, not practitioners. Platform certifications are free, retakeable vendor product exams. The Google Partners badge requires a ninety-day spend threshold across managed accounts and a minimum optimization score, and optimization score is Google’s own measure of how closely an account follows Google’s own recommendations.

So a free-floating opinion that no competent agency would have done this is the opinion that gets excluded or dismantled. What remains is stronger than it sounds. The contract and the statement of work are what the parties actually agreed and are by a distance the best source of duty. The platform’s published rules can establish that a specific act was prohibited by the system the work was performed in. Objectively verifiable facts of execution carry real weight: conversion tracking that never fired, a tag removed on a datable day, budget delivered to a page returning a 404, spend billed that does not match spend delivered. And internal inconsistency — a party’s own reporting contradicting the platform’s record — is often the most durable finding in a matter. I am not aware of a published decision establishing a standard of care for digital marketing services. That is the result of a search, not a proof of absence, and I state it that way in a report.

Writing in public, and the two lists the rules require

A retained expert’s report has to include a list of all publications authored in the previous ten years and a list of all matters in which the witness testified at trial or by deposition in the previous four. For an expert in this field the publication list is unusual in scale, because digital marketing practitioners write constantly — articles, conference material, technical posts. Every item is potential impeachment material, and the list is a rule requirement rather than a courtesy.

I treat that as a constraint on how to write, not as a reason to stop. Pages on this site are written to be read back to me under oath. They concede the limit in the same breath as the capability. They name who holds each record and on what schedule it disappears. Every one of them names at least one thing the available evidence does not settle. Where a case or a statistic is routinely mis-described in trade writing — and several in this field are — I would rather say nothing than reproduce the error, and where a figure comes from a vendor or a trade-body survey I say who produced it, when, and what it actually measured.

The same discipline shapes the engagement file. The facts, data and assumptions counsel supplies are kept as a dated list from the first day, because that category is discoverable and it is far better as a document than as an archaeological dig through correspondence months later.

What I cannot establish

Records show conduct. They do not show intent. Change history records what changed, when, and under which login — not why, and not who was sitting at the keyboard. A reconciliation showing that a client was billed more than the platform charged establishes arithmetic, not wrongdoing: where an agency bought media on its own account and resold it, that gap is the expected result of the agreed structure rather than a deviation from it, and the contract decides which situation applies.

Advertiser-side data cannot identify who generated a click. Platform-side filtering reports show what a platform’s own systems rejected, not what they missed, and the detection logic is not published — which is the first thing an opposing expert will say. Expired data does not come back; no motion recovers a record that aged out of a platform while the parties argued about a protective order. And no analysis of a marketing record tells a court what a case is worth, whether a duty was breached, or how the matter should come out.

Those limits are not modesty. They are the reason the parts I will testify to hold up when someone competent is trying to take them apart.

The engagement record

Working in digital marketing since

1996

Expert reports

36

Depositions

8

Trials

5

Arbitrations

1