Teaching the simple things simply is the hardest thing in the world, approached only by teaching the complex things simply. I don't know the book, but I bet if anyone can do it, he can.
Also, I wonder if the sales guy appreciates how important it is just to watch someone playing -- their attitude, their demeanour, their whatever-it-is-that-makes-them-Pete-Seeger. As was said earlier, just watching Ronnie Gilbert throw her head back and sing, or watching Pete Seeger standing straight backed and playing his heart out... I am second to none in my admiration for cleanly, professionally produced training videos. But 3 minutes of a badly shot video of Son House playing the blues is worth 300 minutes of carefully shot finger positions. (Glad to have them both, believe me, but still...) yours, Peter T.