You did a great job. She might have seemed healthy, but you never know. Say the couple did get the puppy, they get home and the puppy starts to have diarrea. They take her to the vet and he has to put her on medication for a number of things. You probably saved that couple a lot of money. They would have less vet bills and probably found a cheaper yorkie. Don't beat yourself up. You did good.Here is a link to my club against puppy mills. It is called YAP aka yorkies against puppymills.
http://www.yorkietalk.com/forums/group.php?groupid=61