[Ashley V]

Truthfully, I would raise the price a bit and once you chose the people to sell the pups too, surprise them with telling them that they'll get some money back once they get proof of spay/neuter. Also, put a time limit. Say that you want proof by ____ month. It's a win/win situation. You get people that are more sincere by NOT telling them that you refund some of the money once they spay/neuter and it's pretty much guarenteed they'll spay/neuter their pets so there won't be "unwanted" babies running around.