512 clients and 5 years after starting my first agency -- this is almost ALWAYS true.
If a prospect is a pain in the ass during the sales process,
They were a pain in the ass as a client.
Building an agency that is highly profitable (and you/your employees enjoy) starts with client selection
You SHOULD NOT take on clients you can't serve or doubt every word you say.
Just because they're willing to swipe their card, doesn't mean you should take their money.