[cashflyer]

All I can tell you is that the one I used recently SUCKED.
Actually, I can tell a little more than that.

Be sure everything you discuss is put into writing. It's better than trying to remember who said what later on. Or coming up with a "I thought you were going to install a _______ there."

Be sure everything your contractor agrees to do is put into the contract. Not just specific equipment listings, but also all fees - and any "perks" that they promise. If it's not in the contract, it probably won't get done.

If you're doing a major change, have floor plans with notes and drawings. (You don't want a vent to show up on the south wall that was supposed to be on the west wall.)

Be sure to set deadlines, and arrange to make progress payments at certain checkpoints along the way. Never pay in advance.

It always helps to get more than one contractor to quote the job.