Oh my I would have left once I saw the dame/sire being different that expected.
Any breeder that tells you such a fabrication ask her to weigh the adult or puppy in front of you. I have a scale and if any buyer wanted to see that days weight of the puppies or adults I would accomodate their request without being offended.
Money or better said GREED is their motivation knowing the smaller the dog the easier the sell generally and smaller is the demand. Most people buying a yorkie are searching for the 5 lb dog more or less not a 12 lb.
BUT... a yorkie that is 10 lbs or 4 lbs as adult doesnt guarantee it is healthy.
My female was 4.5 lbs before giving birth and now is a wopping 5.01 lbs and my male was 5.5 lbs and now is 5.10 lbs I attibute the weight gain to the food I have them on (royal canin baby puppy food until last week) the adults wouldnt stay out of the baby puppy food and now they are eating Royal Canin puppy food. Once all the puppies leave I am sure they will eat less and will be give Royal Canin Yorkie food, but I dont mind the added weight.
My puppies weight at 11 weeks 3 days are 2.0, 2.25, 2.3 and 2.54....they are very healthy, spoiled wonderful little creatures
and adult size should be 4-5 lbs.