It will happen. Finding a solution for a client is difficult. The only thing that protects you is the contract. We do our estimates & payments based on phases so that we can modify throughout the development process or part ways if necessary (if the client or we are not happy with the relationship).
We had a client once that wasn’t pleased but it was a special situation. They wanted us to break the laws of physics by making a smaller product than the interior components. They went to another firm and had the same problem.
We’ve had to fire a few clients throughout the years too so it goes both ways. Sometimes it’s just not a good fit.
Steppen, just talk to them and hopefully they realize they are not a good fit.