Don't bother replacing the belts yourself. They have to all come off in order to do the idler tire, anyway. Ask if they use the Marrs capstan belt. If not, then supply them. Other cheaper generic capstan belts WILL work, but nowhere near as well, and I've done a ton of them, and it is a huge difference.
Oh good point, I might as well have them do the whole thing at once. Already on it. I'm going to supply the Marrs belts anyway just to be safe.