A certificate image proves almost nothing by itself
A tidy document sent as a photo or PDF feels reassuring, which is exactly why it is weak evidence. Images are easy to copy from another dog's paperwork, crop out of context, or generate for a dog who was never tested at all. The claim itself is what you are verifying: which dogs were tested, for what, by whom, and with what result. So slow the process down and convert every claim on the advert into a checkable fact. If a seller says the parents are health tested, that should unpack into named tests, named parents, and a paper trail that exists somewhere other than the seller's phone.
Get the identifiers that make checking possible
Ask for both parents' full registered names, their registration numbers where they have them, and the specific tests performed on each. Different conditions are assessed in different ways: some are DNA tests with a clear, carrier, or affected result, while others, such as hip scoring or eye examinations, are assessments carried out by approved vets or panels at a particular age. A DNA result for one parent only tells part of a story, and a test done on a grandparent does not substitute for the parents in front of you. A genuine breeder answers these questions from their own paperwork without hesitation, because for them the testing was a real cost and a point of pride.
Check with the scheme, the lab, and the record keeper
With the parents' names and details in hand, go to the source. Many kennel clubs publish searchable health results linked to a dog's registered name, and recognised screening schemes keep records of scores and grades that you can confirm independently. Where a result came from a laboratory or a veterinary practice, the paperwork should name them and carry dates that fit the dog's age and the mating timeline. Match everything carefully: a single differing letter in a name, a result dated before the dog was old enough for that assessment, or a microchip number that does not correspond should stop the purchase until it is explained in a way you can re-check.
Know which red flags end the conversation
Some answers are disqualifying rather than merely disappointing. Certificates the seller will not let you see in full, parents identified only by pet names, results promised later after the deposit, and claims that a breed simply does not need testing all point the same way. So does a vet check being presented as if it were a hereditary health test: a general examination says a puppy looks well today, not that his parents were screened for the conditions his breed is prone to. Walk away without apologising for your caution, because the market improves precisely when buyers refuse paperwork that cannot survive daylight.
Keep the verified proof with the puppy it protects
Verification is wasted effort if the evidence then disappears into an email thread you will never find again when a vet, an insurer, or a future owner needs it. Store copies of both parents' test results, the dates and schemes you checked them against, and the puppy's own first records in one place from the day he comes home. KinsLe's Pet Passport keeps that whole packet together and portable, so the health claims you verified before buying remain provable for the rest of his life, at any vet visit, boarding stay, or handover.