do i give deposit back if buyer backs out?

sold a greyhound pup to a person, after two weeks off mistakes from him putting money in he finally put a 750 dollar deposit in my acc, the dog was to be picked up today but i didnt release dog as waiting for remaining 1000 dollars and now he wants to back out, mind you i could off sold this pup to 3 other people in meantime and gave him an opportunity for his deposit back last week,what should i do