When I had my house painted a number of years ago, I didn't accept the lowest estimate-- I was afraid the guy would get too drunk and fall of the ladder. I still do business with the guy I chose that had the middle estimate.
More recently I ended up using a guy that also came in with the middle estimate for drywall, because the lowest estimate cancelled out the night before the job was scheduled.
Well I've used and fired a fair number of the lowest priced guys over the years. Now I've settled in on those who make my life the easiest and this allows me to get more deals done over the course of a year.