Our Golden Retriever pup came from a breeder locally who breeds several litters a year (from different parents obviously), and also breeds border terriers. I was dubious at first, but when we went to view her latest litter, was pleasantly surprised. Lovely setup, obviously in love with every single one of her dogs, and we saw both Mum and Dad. She asked all the right questions about our home, garden, walks, our experience with owning dogs etc. I checked out the parents on the KC Register, and her other litters. She also has a Facebook page so I contacted a few owners of pups from previous litters and they all gave the breeder an excellent reference. We subsequently decided to buy one of the pups, and I have to say that, 4 months on we are delighted with our lovely girl. Go and visit, ask lots of questions, and, expect lots of questions to be asked of you (if they don't question you, walk away!). It's probably easier to do this before the litter is born, if possible, then you can be more objective and not think with your heart if there are no puppies to fall in love with then and there!
Check whether they have a FB page and if so, message some of the members who post there. Then just go with your gut instinct and trust your own judgement. Good luck x