Buying a Puppy or Dog From a Private Party
You should never "buy" a puppy or dog from a private party. Instead, please see our section on "adopting" a puppy or dog from a private party
The difference between buying a dog and adopting one is the motivation behind the selling/rehoming party. If someone cares for a dog that they can no longer keep for whatever reason, their motivation should be to find the best new home for the dog where the dog can lead a happy life. On the other hand, if they are trying to "sell" a dog, then there is an implied profit motivation, and if multiple people are interested in the dog, are they going to sell to the highest bidder or to the one who can provide the best home for the dog? And as long as there are people out there "buying" dogs from private parties, it creates a demand for these dogs and perpetuates the problem of people stealing others' beloved pets which they then turn around and sell for a profit. A dog is a living being, not a commodity you should buy or sell.
Sure, there are also adoption fees involved when you adopt a dog, but it is only to help cover a portion of the costs incurred by a rescue group or shelter (not a private individual) in the process of rescuing and preparing these dogs for adoption. This is not the same thing as someone trying to sell their own dog (or one they claim to be their own dog). If a private individual is looking for a new home for their dog, there should not be any extra costs involved that they need to recoup from the adopter. That being said, it is fine for a private party to ask for a small rehoming fee to ensure a loving new home for the dog. In fact, they are often encouraged to do so in order to prevent ill-intentioned people from trying to pick up a free dog to use as a bait in illegal dog fights or some other equally horrible thing they plan to do with the dog. The key is that the fee must be small enough that they are not profiting from the transaction.