The Dale Carnegie comparison threw up a red flag for me because that book is all manipulation. I have an ex-friend who read it and swears by it, but she's just become completely insufferable and fake. It's like she's constantly in a job interview.
Is your friend on the spectrum by any chance?
I've read the book and had a visceral reaction to it personally. It is called "How to win friends and influence people" after all. Seems to be a love it or hate it type of thing.
How did that go again?
Dear $FIRSTNAME $LASTNAME,
I am writing you to emphasise how much your business personally means to me and how $EMOTIONAL_STATE I feel about it...
Also remember that he was a huckster, for example changing his name so people would associate him with the steel Carnegies (no relation).