If you're very concerned, you can check if the parents of a litter have been evaluated by the Othopedic Foundation for Animals. (www.ofa.org
) Many issues are genetic, and if the parents have been evaluated, you can expect similar outcomes in the litter.
I've been down this path with our former mastiff. She was clear of lines for PRA and hips. Hip issues and blindness are not fun with a giant.
If the breeder has concern for their pups, they'll spend the money.
You will also pay for it, but it beats many preventable heartbreaks.
I also agree with delaying spay/neuter until maturity.