I have met plenty of people in that line of business who don't know their ass from a hole in the ground, and they do just fine because they talk a big game to laymen. Just because someone does something for a living doesn't mean they are an expert in that field--some "tradesmen" are actually better at being "salesmen", and unless you have some inside knowledge in the industry, you might not know the difference. Your qualifier "apparently" doesn't exactly inspire confidence.

I'm not trying to talk down on you or your guy--he could know, based on what he's seen, that the job is more difficult than most--but don't assume that just because he supposedly takes on big projects that he's not ripping you off.