Working With a Digital Marketing Expert

What this kind of expert is retained to do

A digital marketing expert in litigation is not retained to say whether a campaign was good. That question has no external answer, and an opinion built on it collapses under two minutes of cross. The work is narrower and considerably more durable: reconstructing, from records held in several places by several parties, what was configured, when, by which login, what the platform billed, what the client was invoiced, what the client was told, and where those four diverge.

The output is a reconciled sequence — a dated, sourced timeline — and the opinions are whatever it will bear. That framing matters at retention, because it determines what counsel should ask for. "Reconcile agency-invoiced spend against platform-recorded spend for the period X to Y" is an assignment. "Determine whether the agency overbilled" is a conclusion, and an engagement that starts with the conclusion in the scope has already given the other side something to work with.

This page describes how such an engagement runs, in the order it runs, and what each stage settles.

Names before facts: the conflict check

The conflict check runs first, and it runs on names, not on the story. The test most courts apply to disqualification is generally framed the way the court put it in Wang Laboratories, Inc. v. Toshiba Corp., 762 F. Supp. 1246 (E.D. Va. 1991): was it objectively reasonable for the party claiming to have retained the consultant to conclude that a confidential relationship existed, and was any confidential or privileged information actually disclosed. Affirmative answers to both, the court said, compel disqualification. Other courts state the test with variations, and some add a balancing step for the public interest.

Two operational consequences follow. The check has to run against parties, counsel and related entities — including brands, agencies and platforms the expert may have worked with commercially — before any case facts move. And an exploratory call in which counsel describes the matter can itself create the objectively reasonable belief the test asks about. The Wang court policed the doctrine in both directions, noting that lawyers could otherwise disable troublesome experts merely by retaining them, and that counsel bear a burden to make clear when a confidential relationship is intended.

One wrinkle is specific to this field: experts here often hold live commercial relationships with the platforms whose data is in issue — partner status, certifications, beta access, speaking arrangements. Those are not disqualifying, but they are disclosable, and raising them before retention costs nothing while discovering them at deposition costs a great deal.

Scope written as questions, not as conclusions

The engagement letter does work that the Federal Rules later make visible, which is a reason to write it as though opposing counsel will read it. Several parts of it are discoverable by rule: FRCP 26(a)(2)(B)(vi) requires the report to state the compensation to be paid for the study and testimony, and FRCP 26(b)(4)(C)(i) carves compensation communications out of work-product protection.

What the letter should fix: the retaining party and the matter — retention by counsel rather than by the client directly is the common structure; whether the engagement is consulting or testifying, and how one converts to the other, since the distinction changes what is discoverable; scope stated as questions; the rate structure including deposition and trial rates; data handling, storage and what happens to productions at the end of the matter; and the position on artificial intelligence use, stated up front rather than discovered later.

This practice does not take fees contingent on outcome. Beyond anything else, a compensation arrangement that moves with the result is a gift to the other side at deposition, and the compensation statement is a required disclosure rather than a private arrangement.

The evidence review starts with what still exists

Once the engagement is live, the first substantive question is not what happened. It is what survives. Advertising and analytics records are generated, held and deleted by platforms on published schedules that run whether or not a complaint has been filed and whether or not a hold letter has gone out. None of the major advertising or analytics products exposes a control that suspends deletion.

So the review opens with an inventory: which accounts and properties exist, who owns them, which manager or business account they sit under, who holds what level of access, which payment profile paid, and what the retention position is for each record type in issue. That inventory drives the discovery requests, because a request drafted against the wrong object returns nothing and burns weeks.

It also identifies the losses that have already happened. The single most common irreversible loss in these matters is data that aged out of a platform while the parties argued about the protective order, and no motion recovers it.

The analysis is a reconciled sequence, not a verdict

The analysis phase builds the timeline from records different parties hold. Seven categories carry it: the contract and every statement of work; account ownership and access records; change history for each account; invoices against platform spend; campaign structure over time; communications and approvals; and the reporting the client received, beside the platform's own numbers for the identical period and definitions.

Two reconciliations do most of the work. The first compares what the platform charged, what the account's reporting says was spent, and what the client was invoiced. The second compares the agency's client-facing reports against the platform's export. In both, divergences fall into three classes — definitional, timing, and unexplained — and the discipline is that the first two are eliminated in writing before anything is characterized as the third. Definitional divergences reconcile to the digit once metric definitions, attribution model, conversion window and time zone are pinned; timing divergences arise because platform numbers for recent periods restate after the fact.

What comes out is sequence, sourced and dated. The opinions are what the sequence supports and no more.

The report, and the rule that governs its contents

FRCP 26(a)(2)(B) requires a retained expert's report to be prepared and signed by the witness and to contain a complete statement of all opinions and their basis and reasons; the facts or data considered in forming them; any exhibits that will be used to summarize or support them; the witness's qualifications, including a list of all publications authored in the previous 10 years; a list of all other cases in which the witness testified as an expert at trial or by deposition in the previous 4 years; and a statement of compensation. FRCP 26(a)(2)(C) governs non-retained experts and requires much less — a subject matter and a summary — which is a distinction worth settling early where an in-house marketing director may be offering opinions.

Three of those requirements bite unusually hard in this field. "The facts or data considered" is broader than what was relied on; material examined and set aside still counts, and in a matter where the production runs to gigabytes of exports, the report has to identify what was considered specifically enough that the other side can reproduce the analysis. The ten-year publication list is consequential for an expert who writes publicly, as practitioners in this field typically do: every post and conference paper is potential impeachment material. And the four-year list covers testimony, not retentions.

Admissibility itself is deliberately not this site's subject. FRE 702 was amended effective 1 December 2023; the analysis of what that changed belongs to the sibling search marketing site, which covers it at depth.

Drafts, and communications with counsel

Two protections shape how the file is kept. FRCP 26(b)(4)(B) protects drafts of any report or disclosure required under Rule 26(a)(2), "regardless of the form in which the draft is recorded" — which covers a marked-up document, a shared file and a version in a repository. FRCP 26(b)(4)(C) protects communications between counsel and a reporting expert, with three exceptions: communications relating to compensation; those identifying facts or data counsel provided that the expert considered; and those identifying assumptions counsel provided that the expert relied on.

The clean practice follows directly from those three exceptions. Counsel-supplied facts, data and assumptions go into an identifiable, dated list from day one, so that the discoverable category is a document rather than an archaeological dig through correspondence. That list is also, not coincidentally, most of what the Rule 26(a)(2)(B)(ii) statement needs to say.

One point of currency, since it comes up: Rule 26's expert provisions were not changed by the amendments effective 1 December 2025. Those concerned privilege-log methodology and multidistrict litigation management.

Deposition, testimony, and the rebuttal posture

A party may depose any person identified as an expert whose opinions may be presented at trial, and the party seeking that discovery ordinarily pays a reasonable fee for the time spent responding. Discovery of an expert retained only for trial preparation and not expected to testify is ordinarily unavailable absent exceptional circumstances.

The rebuttal engagement deserves separate mention because it is common in this field and almost nobody writes for it. Another expert's report already exists and something in it looks wrong. That posture has its own deadline structure under FRCP 26(a)(2)(D)(ii) and its own constraint — evidence intended solely to contradict or rebut evidence on the same subject matter — and it rewards a different kind of work: reproducing the other expert's number under the other expert's own stated method, and showing what it does when a metric definition is corrected.

A rebuttal witness who is retained still files a full Rule 26(a)(2)(B) report. Nothing in the rule creates a lighter obligation for responding.

What an engagement of this kind cannot deliver

Three limits are worth hearing before retention rather than after.

There is no established standard of care to testify to. Digital marketing has no general licensure requirement, no mandatory body of practice, and no disciplinary body. The advertiser trade body publishes a media contract template and describes it as "a starting point for the development of a customized contract"; the agency trade body stated in writing on 1 July 2024 that it "does not recognize ANA templates as industry standards." The Media Rating Council runs genuine annual audits — of measurement products, not of practitioners. And a Google Partner badge requires a 90-day ad spend of $10,000 across managed accounts and a 70% optimization score, the latter being Google's own measure of how closely an account follows Google's recommendations. Defensible opinions anchor to the contract, to the platform's published rules, to verifiable execution facts, and to internal inconsistency in a party's own reporting — not to an imagined consensus.

The records do not contain intent. A change history shows that a setting changed, on a date, under a login. It does not show why, who instructed it, or whether it was deliberate, an error, a test, or an automated recommendation applied in bulk.

A poor result is not evidence of fault. Campaigns underperform for reasons that have nothing to do with anyone in the case. Moving from "results were bad" to "the defendant was at fault" without an intervening, record-based causal step is the exact thing this practice exists to argue against.

Frequently Asked Questions

Published 2026-08-12