[fredophile]

It's impossible to say without the specifics of the contract but there are some standard practices that can be assumed. If the contract is for a product, as opposed to time spent, for a product there are usually defined acceptance criteria. A large product will have milestones with their own deliverables and acceptance criteria. Once the customer accepts the deliverable it's considered done and the developer should be paid for that deliverable. If the customer later regrets that choice that's too bad. The customer can usually exit the contract at any point although the contract might specify a penalty for this.