There's your problem. Do not take such a client. I am pretty flexible and have I think an awesome, easy organizer where I ask mostly yes no questions and stuff they should have in their heads or on a drivers license, I never ask them to compute stuff except maybe schedule c expenses by category ... if they have the PDFs for inputs, it takes maybe 15-20 minutes to get through. Clients that refuse to sign an engagement letter or  file an organizer also get a go elsewhere instruction. Some people cannot help but attract problems through their own behavioral tics, their money is never worth your struggle.