There's two shops I would trust, and I did all the above in addition to stopping in without notice and asking for a tour. There was a third shop, and when I stopped in they had a freshly painted bumper face down on the cement floor (checked that one off).
BBB check, references for high dollar work, and find a place that's ran like a true business (not like a guy's hobby or one man show). Make sure you get some references that are one year+, when issues will start showing.
A good shop, that's proud of their work, will be happy to do this because they'll know you're serious about quality and not just shopping price.