Comissionfags, have you ever dealt with revisions by a client? If so, how was it like?

I want to get into commissions but I worry that I won't be able to satisfy the client's needs. And worse case scenario: they ask for a refund if I cannot deliver to their standards.
If it were 2d, then it'd be way easier to revise again and again, but I understand that 3d is a completely different beast and that revisions aren't as easy.