I think what's done is done, and like you said... this baby is going to get so much love from you during his lifetime. So maybe your Vet is right, just look at it like you saved this little guy from an awful situation. You trusted a store employee, that obviously lied to you, allowing you to adopt this Yorkie in good faith (on your part). Just love him and cherish him.
I do have to say though, that I wish more than anything, that laws be instituted banning the sale of these animals in pet stores. I mean they get plenty of business selling goldfish, supplies, food, etc.......
Lauren