I was a kennel club breeder, so I know how things go tho not on your breed.
I would advice to def go with assured breeders, tho I want to say anyone can join the kennel club, so just cos kc reg doesn't meant they are good! check out there place, make sure you know all the issues your breed can have and get them checked. Ask for your details to be passed to propel who have bought puppies so you can ask and check info. I never minded people asking this as I had nothing to hide and new my puppy owners would happily chat away about their experience.
Expect to be interviewed, I always checked buyers out. I asked loads off questions, if I was happy I would then interview them explaining that didn't mean they would get one of my puppies. I would then decide after chats etc. if they were right for my pups. Expect to be asked to come a few times to see the pups get to knows them, often a breeder will recommend which puppy is best for you. Plus don't expect to see the puppy befor 4/5 weeks or get the puppy early, I never let mine go before 9 weeks and only if they were ready. You need to ask how they socialise their pups.
Mine were introduced to mixes, children, taken out in arms to hear buses, see traffic, learn to walk on carpets, wood floors, grass, concrete, sand etc. introduced to other animals, bikes, scate boards, prams you will be amazed what a good breeder will do to make sure the pup is properly socialized and used to.
Plus you will often find a good breeder has a waiting list, if they do then don't be upset and go somewhere else, if there's a wait list it's worth joining it.
See the pedigree and champains, see if any previous litters are being show.
DONT assume just because a dog has a pedigree it's good, that's most definitely not thee case, I've known and seen dogs from puppy farms shipped to breeders and added to litter so they can get a pedigree.
If the breeder just let's you go there no questions, or your not happy, something is niggling... Don't buy the dog, it's easy to fall I too the trap, awww so cute, can't leave them, buy and regret maters when you have unruly pup with no socialising and big issues that won't show till older.
I know as I have a x puppy farm dog, he's lovely but has issues and even with all my work etc he's still got probs.
I've added a pic of 4 of my pups, was always so hard to see them go, but I near from the owners even had painting sent to me of them..
Ok sorry long winded and do message me for more info, I'm hoping some of this helps.
Wanted to add, yes there should be a contract, receipts, copies of pedigree and all info of medical records, take your pup within 24hrs to a vet for a good check, some vets will do this for free, I bought a stunning pup once from a breeder who was well known, turned out she had a jaw defect which would take thousands to correct and also was then no good for breeding plus a possible hereditary issue, so hard as was she went back. Your breeder should in contract state a full refund within 48hrs of issue if medical issues are found, tho they may want a 2nd opinion, this is normal.