This is complicated. I audited a shopping center in Raleigh two years ago (no longer my client). Now I'm working with Duke Energy on a different matter. The shopping center is suing Duke and their attorney wants me to testify about billing errors I found during my previous audit. Duke is currently my client on the other matter. Major conflict?
Former client asking me to testify against current client
Yes, that's a clear conflict. You can't testify against a current client even on an unrelated matter. It damages the trust relationship.
I had similar situation in Phoenix with APS. Had to decline the testimony request. Attorney wasn't happy but understood when I explained the ethical issues.
Could you refer them to another qualified auditor who could review your work and testify instead? That way the shopping center still gets expert testimony without your conflict.
Document your decision carefully. Send polite letter declining due to current professional relationship. Keep copy for your records.
Been there. Had to turn down $5,000 expert witness fee because of current client relationship. Sometimes doing the right thing costs money short-term.
Conflicts of interest can destroy your credibility with all parties involved. Better to maintain clear ethical boundaries even when it means lost revenue. Your reputation is worth more than any single fee.