I don't think you are being selfish or overprotective at all. You are doing what is best for your puppy. Finding the best possible home for him. Who's to say that puppy from the pet store doesn't have parvo and they both get very sick and possibly die. I totally understand where you are coming from and I would have made the same decision! They live in an apartment? are they even allowed to have more than one dog? They obviously have no idea what they would be getting them selves into.
Great job and very responsible on your part. IMO
