Not advice, just what I have run into and what I would encourage people to actually read in their own policy rather than assume.

The general shape of professional liability coverage is that it responds to a claim arising from a negligent act in the performance of professional services. Several things commonly sit outside that.

Fee disputes. A client who disagrees with your savings calculation and refuses to pay is not usually a covered claim. That is a contract matter, and it is the most likely dispute in contingency work.

Anything characterized as a guarantee. If your marketing or your agreement promises a specific recovery, an action on that promise may fall outside professional services and into contractual liability, which is a standard exclusion.

Work performed before the retroactive date. If you have carried claims-made coverage continuously this is fine. If you have had a gap, or you switched carriers and did not buy prior acts coverage, older engagements may be uncovered.

Work performed after you stop practicing. Claims-made policies respond to when the claim is made, not when the work was done, so winding down a practice without tail coverage leaves years of completed work exposed.

Subcontracted work, if you use other auditors and the policy does not name them.

Read the definition of professional services in your own policy first. It is usually narrower than what you actually do.