While I'm not disagreeing with needing to say no to a client, the moment you figure you know everything they want or more importantly, need, YOU are the one with the problem.
There are numerous examples of programmers/providers figuring that they know what the customer needs. They're called enterprise software.
There's a difference between telling people what they want and telling people that they want something that they don't want. You have to listen to them. But bear in mind that if they
