I am seeing a good many young puppies, 3-6 months old, who are moving backwards away from you, snarling, growling and even biting. The last thing a puppy that young should be thinking about is snarling, growling or biting aggressively, puppies should be eager to meet everyone.
Sometimes this is a genetic issue, that means you really need to know as much as possible about the dogs your new puppy comes from. Meet the parents of the puppy on one of your visits to see the litter. If you are told that one or both aren't friendly that would be red flag #1.
Puppy/Dog proof your house
There is always a lot of talk about kid proofing you house when the little ones are beginning to crawl and walk, but the same kind of work has to be put into proofing your house for a puppy or young dog.
Destructive chewing and eating things they shouldn't is a way of life for puppies and young dogs. They will eat potted plants (real and artificial), kids toys, socks, shoes, paper, basically anything that isn't nailed down and they will chew on the stuff that IS nailed down.