You can not guarantee the size for sure. Both my babies I also got from the local paper. My Cody does weigh 15 lbs but also according to the charts he should only be about 6 lbs. However I too am glad that he ended up being bigger because of my boys. I actually tell people that I think he is bigger in self defense
My new girl I just got her a couple months ago was $800. I went and met the lady and saw her home and saw the parents. I actually talked to her on the phone for a few days before I went and saw the house and the pups. I got a very good vibe from her and she is just the nicest person. I actually still talk to her via email and I send pictures. We talk about all sorts of things.
IMO if you are not interested in showing the dog and if champion lines are not important to you and you just want a pet. Then go local. An $800 yorkie is just as loveable and cuddly as as $1200 one. Not trying to offend my any means so please don't take it that way. But if you think you want to "show" or if the "champion lines" are important then by all means find a reputable breeder for your baby.
Don't get me wrong though there are plenty of nice and good people out there who are not "breeders" who take care of their pups and just want them to find great homes.