I've been around this hobby a pretty long time and have not really had any bad deals. I've bought plenty of hets and even possible hets that have proved out. But then again I always ask a lot of questions from the people I'm doing business with. There are people out there that really don't know very much about genetics. It's not because they're dishonest, it's because they're ignorant. So, I ask a lot of questions. Even questions that I already know the answers to, maybe especially questions that I already know the answers to since the answers you get back to basic questions will tell you a lot about the knowledge of the seller.
I guess I prefer to assume that people are honest until proven otherwise. And if you are planning on buying breeding stock without yourself having a firm grasp of how the genetics work, you've really got nobody to blame but yourself.