I have fostered dogs for a long time.
Right now I have a Yorkshire Terrier, Reno, I am fostering. He is ready to go to his forever home and we may have a couple that is going to adopt him.
It is rewarding. Reno was a puppy mill seizure.
You can read Reno's story here:
http://www.yorkietalk.com/forums/gen...ing-today.html
How the Yorkie will be depends on what environment they were taken from. Reno was from a puppy mill and had spent his whole life (8-10 years) in a cage. He just needed love and attention and he is doing fine - except for housebreaking. He plays with Beamer and he discovered a toy he likes to play with the other day. (I took a video of him, but can't post it as it isn't a Youtube)
His coat was very dry through neglect, but now it is shiny.
I have a Reno album on my profile.
I have also fostered dachsies that were puppy mill seizures. One had a club foot. I ended up keeping her and some of the others. Two I kept, I had them for 10 years, and considering they were around 7 and 8 years old when I got them, that is a good age for a puppy mill rescue.
If Reno is adopted this week I will be getting Clover, another rescue from the puppy mill. The rescue group want me to take Clover as soon as I can. But we feel we need to rehome Reno first, we are not as young as we were, so two rescues at once on top of our own two would be a little much.
You will be doing a wonderful thing for the little Yorkie if you agree to foster it - and you will find lots of advice and help here if needed.