Welcome to the forum and to NH!
I don't really hear about waterfowl guides in NH. I am sure there are some, but ME, MA, RI all seem to have more on that front. There may be some sea duck guides, but as with above, most are not in NH.
As you know, NH is pretty hunter friendly, but we are far from the duck capital of the flyway. Lots of spots to hunt but scouting (and lots of scouting) is what helps.
I am self taught. My dad/grandfather taught me fishing but waterfowling is 100% me. Reading the forums helps, but going out and trying things is the only real way. Hours on google earth scouting spots, hours driving and gallons of gas scouting. It pays off.... sometimes...