Depends how bad TP’s records are. Have you obtained W & I transcripts? Problem with lack of support often arises when TP has SE income and cannot support tax deductions. Look at Circular 230 and if you are a licensed practitioner, look at your ethical requirements. It may ethically make sense to walk away from such a client. Also consider what TP has as support and look at IRS disclosure requirements. I believe the IRS disclosure form is 8275.