I think alot of dishonest breeders live on the hopes that they can fool you about the health of a pup/dog upfront and by the time you have had it vet checked, you will be too attached to it to give it up, allowing them to keep your money.
I met a breeder when looking for Trixie who tried to sell me...well, I don't know WHAT she tried to sell me...and told me just to take it home and if I didn't fall in love with it she would give me my money back.
Needless to say, we high-tailed it outta there!