I will put my two cents worth in here. You are worried about getting a healthy dog, then you need to focus your questions, on how well the breeder knows her line and the health problems within her line.
You should get the registered names of both sire and dam and their registration numbers; with this information you can look up what health tests have been posted:
www.offa.org, for hips/elbow (Xrays that are evaluated to see if the dogs are clear of dysplasia, CERF will be posted there as well, this tests if either dog suffers from a congential eye problem such as PRA or cataracts. LP - luxating patella should have an evaluation from a vet. A relatively new site call CHIC,
www.caninehealthinformation.org, will accumulate all tests done on a particular dog and show the results, the dog will receive a CHIC number once all the required tests that YTCA asks for are complete.
Please know that the breeder should be more than willing to share the registration number and official names of the breeding pair. If not, if there is any demurral I would be very hesitant to go forward with a purchase.
Also if the breeder says that "oh yes I test my dogs", and yet you can find no information on the various health sites I listed above, then you really need to ask why hasn't she posted the results? There is rarely a good reason for not posting good results.
Both sire and dam, should have been BAT tested Bile Acid Test. This helps to determine if the liver is functioning properly. YT's have a high incidence of Liver Shunt (LS).
As well both breeding pair should have had some further pre breeding tests.
I know this is a lot of information to take in, but you did say you want to do your best to secure a healthy pup this time around.
Now unfortunately none of the above tests, are true genetic tests, all they can tell you is that the parents are free of any of the aforementioned diseases. How-ever that is a very important point. Breeders should be breeding healthy dogs. It does not guarantee that your pup will be healthy, but it does offer the best chance that your pup will be!
I would want my pup to be BAT tested prior to picking him up. Usually best done at 16wks of age, although can be done earlier. The test needs to be repeated at 6mths of age.
If you have any questions about the health tests, just ask, I'll be happy to help.
Best of luck in your puppy search.