I've only had one truly bad experience buying used. Overall it's a good way to save money provided you can trust the seller.
If you have your own ball spinner, Abralon pad and polish collection, it's absolutely a great way to save money. That way, you need only pay, at most, for a plug-and-redrill of the thumbhole (provided you like the layout already on the ball) and two new finger inserts. You can handle the resurfacing yourself at home. If you can do your own plugging, it gets even better.
I've got a full backyard shop with drill press, so it makes a lot of sense for me.
If your pro shop charges very high a la carte prices for plugging, redrilling and surface prep, though, I'd advise you to stick with new balls unless you find someone who has an equal span and/or only sells low-game-traffic balls.
Jess