It may not be his fault but these are clearly unscrupulous people! You need to try and report them/sue them whatever you can because chances are you are not the first person they've done this too! It happens quite frequently to the point where in my state (New Jersey) we have laws protecting people against it.
Research puppy lemon laws, contact your local SPCA and ask for help. They've probably done this to loads of people. When you purchased him, did you pick him up from the house? Or did you meet the people in a parking lot somewhere? Did you meet his parents and littermates?
The pup may be lucky to be with you now, and my reason to not return him would be I'm sure as soon as you give him back to these people who are clearly NOT ethical breeders, he's going to be killed before you even get in your car to go back home