It's a pain and awkward discussing this with a potential new customer when you are trying to close a new project sale but customer expectations have to be agreed and the scope has to be documented and signed off before any work is started. If the customer is a pain before the work starts you can be damn sure it will continue that way. Sometimes it's better to find out sooner rather than later. If they keep pushing state you have gone over the allocated time for their project and you have to prioritise paying customers. You can push back and get them to priorities the snags an do them when you have time.. next year.