just general talk, ask about yrs in business, how far they are out, how does he handle warranty work, is he one of those that never gets on the roof, etc. feel him out, dont sign anything, do your homework and research.
do not bother checking references he provides, a broken clock is right twice a day. instead use his name and company to run a search. check angies list, etc. you can bend over backwards but out of 100 people 2 wont be pleased no matter what, remember that.
i roof for a living, and you can spot those people you cant please a mile away. if you hang in there, they will be somewhat happy, but it wont go off like clockwork i guarantee. like for instance having to rip off half a roof because they decided on a last minute color change but didnt talk to you. sit and watch you lay half a roof and then say something. yeah, the contractor ate the cost of replacement shingles to keep them happy. i personally am not a contractor but i do sub work now and then, but i wont work for a contractor who wants to do a job halfazzied