pud1
You should expect the breeder to give you a thorough grilling about you, your family, your house, your lifestyle. They should ask what you can offer a dog, why you picked that particular breed and why you picked them as a breeder.
Most (though not all) breeds need at least some health testing so check what tests should have been done (you can find a list for whatever breed they are here) and ask to see the official certificates. They should be able to provide copies of the certificates for the stud dog as well. If they're KC registered and you have the parents full names you can also look their test results up here on the KC site.
Ask why they chose to breed from that particular bitch and what made them choose the stud dog they used. They should be happy to discuss both and be able to explain what about the stud dog compliments their bitch or improves on her weak points.
I prefer to see that both parent dogs have had some kind of independent evaluation so showing, working, dog sports, temperament testing, etc. so I would ask for information about that.
The breeder should be actively raising them as they get older, not just leaving the bitch to it. There's all sorts that a good breeder can do before they go to their new homes to help them become well rounded dogs. Have a read through the information on this site, it'll give you a good idea of the things a breeder should be doing to help prepare the puppies to go off to their new homes at the appropriate age.
Ask whether they use any kind of of puppy contract and have a look at it if they do. It should state that in the event of you no longer being able to keep the puppy the breeder should be contacted first and they will either take it back or help you find a suitable new home. If they don't use contracts I'd expect them to make this very clear verbally. Also, if the pups are KC registered ask if they have endorsements in place, this means any offspring from them could not be registered with the KC until the endorsement has been lifted by the breeder.
The bitch should be happy and apparently healthy, as should the puppies, and the breeder should be raising them in the same way you intend to keep them, i.e. if you're looking for a family pet then you don't want them being raised out in a kennel or outbuilding.
It shouldn't be a case of you just looking at the puppies, deciding you want one and the breeder being happy with that. The breeder should be satisfying themselves that you are worthy of having one of their puppies. The first time DH and met with the breeder of our whippets was more intensive than some job interviews I've had 