The essentials
- Definition: a marketing performance audit measures, channel by channel, what each euro spent produced over a period of 6 to 12 months, and identifies the gaps between objectives and results.
- Seven sections: scope and objectives, data reliability, performance by channel, cost per result, journeys and conversion, sector comparison, a prioritised action plan.
- The deliverable: a 15- to 30-page document plus a reusable dashboard, never a raw export.
- 2026 pricing: €1,500 to €4,000 for a single-site small business, €5,000 to €15,000 for a multi-channel account with e-commerce.
A marketing performance audit is neither an activity report nor a technical audit. Its purpose is singular: to say what each channel produced against what it cost, and why. Many audits sold in 2026 remain annotated GA4 screenshots. Here is what an audit grounded in KPI should actually contain to justify its price, section by section, with the questions each must answer.
Section 1: the scope and the original objectives
An audit with no reference objectives can conclude nothing. The first section recalls the objectives set for the period (revenue, enquiries, appointments, sales), the active channels, the budgets committed and the targets per channel. If no quantified objectives existed, the auditor reconstructs them from the history and says so: that is already a first finding. This section also lists the data sources used (GA4, Search Console, Google Ads, Meta Ads, the CRM, the Google listing) and the period analysed, generally a rolling 12 months to smooth out seasonality.
Section 2: data reliability
Before reading a figure, you have to know it is right. This section checks the measurement plan: conversion events actually firing, duplicates, Ads conversions imported into GA4 or not, consistent UTM parameters, consent and the loss rate tied to the cookie banner (often 25 to 45% of traffic unmeasured in France in 2026). A serious audit quantifies that gap and corrects the metrics accordingly. The verification method is detailed in auditing a GA4 account.
| Control | What is checked | Frequent anomaly |
|---|---|---|
| Conversions | Every business objective has a single key event | A form counted twice (the click + the thank-you page) |
| Campaigns | The UTM source / medium / campaign naming | Meta traffic classed as "direct" or "referral" |
| Costs | Ads spend imported into the marketing platform | ROAS calculated without the agency fees |
| Consent | The share of sessions lost to refusals | A fall in traffic read as a fall in business |
| Filters | Internal traffic and bots excluded | The team's sessions inflating direct traffic |
Section 3: performance by channel
This is the heart of the audit. For each channel (SEO, SEA, organic social, social ads, email, the Google listing, affiliates), the auditor presents three levels: volume (sessions, impressions), quality (conversion rate, engagement rate) and result (enquiries, sales, attributed revenue). The metric that counts is the result, but volume and quality explain why it rises or falls. Each channel gets a rating and a comment of two to five lines at most. The metrics by channel are listed in the advertising campaign KPIs.
Section 4: cost per result and return on investment
This section brings everything back to the euro: cost per enquiry, cost per customer, return on investment by channel, including the hidden costs (internal time, tools, suppliers). It compares those costs with the margin per customer to say whether a channel is profitable, breaking even or loss-making. The calculation is explained in how to calculate marketing ROI.
| Channel | Observed cost per enquiry (small services business, 2026) | How to read it |
|---|---|---|
| SEO | €5 to €30 | Profitable once the site has content; a deferred effect of 4 to 9 months |
| Google Ads Search | €25 to €90 | Profitable if the margin per customer exceeds 3 times the cost |
| Meta Ads | €15 to €60 | Varies with the quality of the enquiries; to be checked in the CRM |
| LinkedIn Ads | €80 to €250 | Justified only for a high B2B order value |
| €2 to €10 | Often the best ratio, limited by the size of the list |
Sections 5 to 7: journeys, comparison and action plan
- Journeys and conversion: where visitors drop out (entry pages, forms, the basket), with the rates at each step. See analysing a conversion funnel with GA4.
- Sector comparison: your rates against your sector's ranges, without claiming a precision the benchmarks don't have.
- A prioritised action plan: 8 to 15 actions ranked by expected impact and effort, with an owner and a deadline. Without this section, the audit stays a set of findings.
Format, duration and 2026 pricing
A usable audit fits in 15 to 30 pages, with a one-page summary at the front for the leadership team. It comes with a dashboard the company keeps after the engagement, so it can track the same metrics over time. Allow 5 to 10 days' work for a small business, or €1,500 to €4,000; €5,000 to €15,000 for a multi-channel account with e-commerce and a CRM. The "free" audits offered by agencies are sales documents: they list problems, rarely quantified results. For choosing the supplier, the criteria are in choosing a data marketing agency.
How GreenRed helps
Rather than juggling several tools, GreenRed's Overview module brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
What is the difference between a performance audit and an SEO or SEA audit?
An SEO or SEA audit examines one channel in depth, with its technical aspects. A marketing performance audit covers every channel at the same level and concentrates on the result against the cost. It refers you to specialist audits when a channel has a structural problem.
How often should you run a marketing performance audit?
A full audit every 12 to 18 months is enough if a dashboard tracks the same metrics between audits. An audit is also called for when changing supplier, redesigning the site, or increasing the budget by more than 50%.
Can this audit be done in-house?
Yes, if someone has a command of GA4, the advertising platforms and the calculation of cost per result. The internal risk is a lack of distance from the channels the same team runs. A middle route is to prepare the data in-house and give the analysis to a consultant for two or three days.
What data should you give the auditor?
Read access to GA4, Search Console, Google Ads, Meta Ads, the Google listing and the email tool, a CRM export with the source of each customer, the monthly budgets by channel and the suppliers' invoices. Without the real costs, the auditor can't calculate a return on investment.