
As the others have said if the case is as desribed and you were being charged full price for the puppy then this sounds suspect to me to.
Now it may be that what was being described was a sale on 'Breeding Terms' which usually means you are getting a puppy at reduced price with agreement to let the breeder have a litter later. These arangements have to be put in writing as th3ey are very variable. soem the breeder takes the dog back for mating and rearing of the litter and then the bitch would go home after the agreement has beeen fulfilled with papers transfred to the new owner. In other cases you are expected to breed the litter at your own expense with the breeders choice of stud, and ghive the x number of pups from x number of litters.
Personally I don't like Brteeding Terms arangements as they often cause ill will and misuynderstanding.
If a breeder really needs to have a bitch or dog back to incorporate into their breeding program then they can always offer the owner of a male a stud fee in the usual way or arrange for a 'Loan of Bitch' agreement whereby the breeder can breed a litter from the bitch owned by you and for the purposes of that litter will figure as the breeder. I bred one litter this way and paid the owners a fee (the price of a puppy as they would have if I paid them a stud fee for a male). They had wanted their bitch to have a litter and have a puppy from her but were unable to do it themselves due to husband working and wife not being in good health, but in the event they didn't have a puppy as by then they couldn't have reared a pup until he retired.
To safeguard their breeds and lines many breeders put restrictions on the pups paperwork to prevent pups being registered (agreeing usually to lift these when health checks are carried out and dog is suitable for breeding), but some feel they need to withold paperwork altogether, as this restriction would only prevent pups being registered but wouldn't prevent the ancestry deatails being used to sell unregistered pups or registering with one of the puppy farm registries, and they don't want their lines being involved with such practices.
I would personally contact the Breed Club/s and find out what this breeders reputaion is. they may be a top notch breeder being super careful and offering a breeding terms arrangemeent on pick of litter, or may be someone trying to have it both ways as hgas been suggested by other posters :D
Good luck.