Both have a place. The difference is depth and accountability.
What a good free audit gives you
A focused review of your highest-traffic templates, three to five concrete issues with evidence, and a rough revenue estimate. It should be useful even if you never reply.
What it cannot include
Analytics validation, session-recording analysis, competitor benchmarking or a prioritised roadmap. Those take days, not minutes.
What a paid audit must include
Data verification, funnel analysis by device and source, qualitative evidence, prioritised recommendations with expected impact, and implementation guidance.
How to spot a weak audit
Generic findings that could apply to any store, no reference to your actual numbers, and pressure to sign before the findings are explained.