to YT.
Hopefully you can see the pup's parents, & ask if the parents are AKC or equiv. registered, & if the pup can be registered, i.e., the breeder will provide the registration papers.
Also, look at photos of Yorkie pups, at about the same age as the pup you are interested in so you know what a Yorkie pup should look like. Likely easier said than done.
Good Luck.