Nothing says more about a company than how quickly they return customer phone calls.
One missed appointment is probably acceptable as long as the contractor did his best to contact the homeowner, but more than one is an indicator of the contractor's potential unreliability. Product knowledge is hard to fake. A good contractor knows that well-informed consumers turn into satisfied customers, so ask questions. A good contractor will listen to your ideas and plans, and advise you on how to best accomplish them. Your contractor should provide intelligent ideas, creative thinking and good advice.