7 lbs and under is the "standard" for yorkies. 7 is still really small! My Thor is a little under 4lbs, and many people say he's the tiniest adult dog they've ever seen. I wish he were a little larger, honestly.
I agree with people here, focus on finding a reputable breeder. Their goal will be to breed yorkies 7lbs and under. Some of them may be larger, some smaller. A very good breeder who knows her lines will be able to give you a better estimate (not guarantee) of size.
There are a lot of unscrupulous people out there who promise tinies. They can use all kinds of tactics - pretending a dog is older than it really is, so it seems to be small; pretending they know the dog will be small, when they really have no idea; or most tragically, breeding very small, unhealthy dogs with no regard for anything but size.
The word "teacup" is a big red flag. A good breeder will not use this term.
Good luck on finding your new baby.
