I like people who are communicative. I've worked with some breeders that I wouldn't hesitate to buy from again and then I have worked with breeders who are some of the first people I will check if I am looking for something new. The guy I got my Hypo Jungle Boa from is one of these people. I had such a great time working with him in the process of purchasing my little girl then I sent him an update e-mail about 6 months later to show him how her color is progressing and how nice she still is. He in turn was happy that I was taking such good care of his girl that he offered me a great deal on a male that he is holding for me until the spring.
I tend to buy what I am looking for even if it's from a breeder I don't know much about. They don't have to have a good guy BOI but I do check for bad ones. Getting scammed is not high on my to do list.
Really for me though it all comes down to how communicative they are, how well packaged my animal is when shipped, is the animal healthy and was the animal accurately represented. I'm used to my reptiles wanting to bite me so I never even bother to ask about temperament. Feeding documentation is always a plus but I haven't received that with any I have purchased so far so I'm used to not getting it but I plan to send it out with any I sell.
I also will never buy from anyone who has rumors or proven cases of shipping mite infested snakes again. With all the breeders out there it's not hard to find one that won't send me a snake with mites.