My fiancé bought my engagement ring from a jeweler in New York. Long story, but essentially he did kind of a crappy job and made it over a size too big (even though he measured me--he just ignored that and made it in the wrong size).
It's a pain for us to get to NYC during the week, but my ring really needed to be sized. I took it to Robbins first, since we had looked at rings there when we were first looking. Since the ring was so delicate and not super well-made, they were nervous to size it and recommended that I take it to John at D'Antonio & Klein.
John is fantastic! He sized my ring right in front of me while I waited. He told me everything he was doing and when he took it upstairs to be cleaned he said I could go up with him if I felt more comfortable with it not leaving my sight (I declined). When the ring was finished being cleaned, it looked even better than when I had first gotten it.
I noticed the next day that the center stone was a little loose (this often happens when a ring gets sized) and I took it by the next day and he sized it right away.
He is super knowledgeable and honest. We will definitely have him make our wedding bands, and any other fine jewelry we buy in the future.