I think I said this before, but the first time I had a yorkie, I had babysat him for a friend of my sister over christmas. KJ was 3# and 3yoa. His owner asked my sister if I wanted him as he was always filthy, wasn't potty trained (he thought a dog wouldn't potty in his cage). He was a college student with two jobs, living in a highrise apartment building in downtown dallas. He kept in this tiny cage almost 100% of the time. I said 'potty training requires the dog have a chance to potty elsewhere.' He was really a nice boy, I am not sure where he got KJ or how long he had him; I was just glad he gave him to me.
I found him to be perfectly potty trained. He lived in my lap or at my heel all the time.
Make sure he knows they can become hypoglycemic, needs food and WATER - ALL the time. Maybe you could offer babysitting service in case he needs to go on vacation or something.