
Buying a puppy is a major decision and as you know not undertaken lightly. It is good you are being so cautious. I always advise people to work out what questions they want to ask and write them down.
This serves two purposes,
1. You don't forget to ask something important such as asking to see the British veterinary Association health scheme certificates for the sire and the dam of the pups.
2. You don't get sidetracked by chatting or cuddling puppies.
Make sure you understand what the breeder is saying to you, about the breed, caring for your pup etc... Most breeders will offer you a contract of sale, which should state exactly what you are getting for your money. It may cover health as well. As the other poster here has said look for signs that the other older dogs if present look happy and healthy, are confident and not nervous.
Look at how the puppies are kept and if they are happy and healthy. Do they have watery eyes for example? If so it may have entropian, a condition whereby the eye lashes turn in rub the eye.
Many breeders these days will get their puppies checked before sale by their vet. Some breeders will do a first vaccination and all breeders should worm the pups before they go to their new homes.
To find out what health problems may affect the breed you have chosen, go to your vet before you visit have a chat with him/her and ask what questions you should ask. Your vet should be able to tell you whether or not a breed needs to be hip xrayed, elbow xrayed or eye tested for example.
Good luck and let us all know how you get on.