That's why it's not just about showing but about health checking (DNA testing, eye testing, hip testing, etc etc).
A health guarantee till two years of age is nothing, especially since most of the time they'll either refund you (in exchange for the dog) or give you another puppy (in exchange for the dog), and especially since a lot of the genetic issues occur later on, and not before 2 years of age.
Good luck with your puppy.