I am no "pro" here but here is what I would look for (I work at a shop and know what some shops run into which hold things up or turn into problems)... Look at the work that is there currently and ask them how long they have been sitting there for. See how clean the shop is and how organized they are, reason for this is because you do not want them tearing your car apart to paint it and then lose something and they lie to you saying that you never had the part to begin with. Talk to the employee's of the shop, see if they know what they are talking about or if they are just some jo blow off the street wanting some crack money (trust me on this one, especially in our area here we have had lots come looking for jobs). See what kind of materials they use and look at how clean their spray booth is. I hate to see shops (even we do it sometimes because of the customer) that use all these different brands of materials for paint, primer, sealer, etc because they will cheap out on one big time like primer and base and think that a really good clear will cover for the two.
Just look at the cars that are there and see how they are stripping them down and look at the gaps of the cars to see if they take time on the detailed things like gaps and jambs of a car. Now when I say this though I dont mean to look at a Honda Accord or something, I am talking about a high end paint job that someone paid a lot for or a old hot rod that is going through a restoration.
I can't really think of anything else right now besides to talk to the boss and see how confident he sounds in the time it will take, the money it will cost you and how confident he is in his work.
Good luck and let me know how it goes!