This is a few years old, so there may be some changes, but it does a good job of explaining preparer penalties. https://www.thetaxadviser.com/issues/2017/feb/preparer-penalties-sec-6694-6695.html
When you prepare and sign a return you are stating that it is true and correct. If there is reasonable doubt, I wouldn't sign.
If client can not provide financial statements that make sense, I will tell them:
1. Where I have issues for them to try to fix them or
2. That they need to hire a qualified bookkeeper or
3. They need to provide me with all documents to create accurate statements, or
4. Go somewhere else
If they don't take any compensation and come to me after year end, I may or may not prepare one return based on that with a clear understanding that they immediately start taking compensation. If they appear to have a genuine interest in doing so, I'll likely prepare the return. If they want to argue with me, I'll decline the engagement. Same thing if they take what I believe is substantially lower than reasonable compensation.
Remember that clients talk with other business owners. If they see that they can push you around to doing things the way they want rather than what you know to be an accurate return, they will tell others. Do you want your business built on a client list like that?
I've walked away from quite a bit of fees over the years if the potential clients didn't live up to my expectations. I've also left jobs where I was the internal accountant and pressured by owners to provide misleading financials for bank or tax purposes. One of the main reasons I started my own firm was so that I am the one making the decisions that effect my integrity.