First thought, from what you stated this guy would appear to be a finish carpenter. They do great work and are very meticulous at what they do (cabinets, trim, etc.), but I wouldn't hire one to do a deck unless you wanted it highly polished. Second thought, get a couple of more estimates from "regular deck builders", look in the phone book, drive around to new construction sites and find someone actually building a deck. Talk to them, either about building the actual deck, or putting up the deck frame as you mentioned. The price per foot for just doing the frame and joists will be a bit higher than if they were doing the entire deck (travel, only a couple of hours of work, etc., versus being on site for a day or so). Third thought, learn how to do the entire project, find a high school kid (strong) wanting to earn some cash for a weekend's work and do it yourself. The stronger and younger the kid, the better they are at digging the holes (manually).