Always ask to see pedigree papers of the parents and ask to see a certificate to say that the breeder is registered with a particular Cat Council.
HCM testing is another area of consideration - ask the breeder if you can see copies of paperwork from a Board Certified Cardiologist. This will be paperwork of the Sire (father) and Dams (mother) HCM tests signed and dated by the Cardiologist - it must be of the parents of the kitten you are purchasing and that they were clear of HCM and a current date - ideally yearly testing.
There are also many "Scams" being advertised on the internet, I have had some upset people contacting me that have deposited large sums of money into bank accounts with no kitten ever arriving and never hearing from the seller again. The old saying - if it sounds to good to be true then it generally is!
Be careful also when buying outcross kittens. Do your homework to see what the Sphynx has been outcrossed to - also ask what is the particular reason the breeder has decided to do that particular outcross.
The information below is from a Sphynx breeder who also breeds Devon Rex. She has been breeding Devon Rex for the last 30yrs. These are the reasons why she and many other Sphynx breeders will not outcross a Sphynx to a Devon Rex or other mutations.
If I breed, exhibit or sell a kitten and call it a Sphynx, I want to be sure that it is just that and not a Hybrid.
Using a Devon Rex outcross is a quick route to getting a hairless kitten - it can also be a quick route to doubling up on HCM, on introducing Inherited Myopathy, blood group incompatibilities, coagulopathy problems, luxating patallae and hip dysplacia. There are other healthier choices available, they just take longer to develop the hairlessness.
With permission from Ann Hobson-Kelly Nobilero Sphynx & Devon Rex Breeder UK