Of the roofers who knock on your door, the ones from far away are the most risky IMO. If there's a problem with the repair, good luck getting them to come back and fix it. I'd be comfortable giving the work to a local contractor who has been in business for a good number of years, even if he/she knocks on the door. Expect all sorts of tactics: a friend in a hail-damaged area reported a parade of very nice looking ladies knocking on his door soliciting business. He said their accents often revealed they were not local.