Ask the breeder why they breed Siamese?
A good breeder will never hesitate to explain why they breed Siamese. I don’t actually know any breeders who won’t talk for hours about their beloved Siamese. Most breeders will go on and on about their favourite breed to the point where they start to bore you. If a breeder doesn’t seem interested in extolling the virtues of their cats to you or if they aren’t able to tell you why they breed Siamese, then I would certainly question their love and knowledge of the breed.