Les Giblin

Sold for years in the field and then ran his own sales training business, and How to Have Confidence and Power in Dealing with People came out of that in 1956.

The core claim is that people are interested in themselves, so the entire skill is redirecting attention outward: ask, listen, and let the other person be the important one in the exchange.

Giblin is plainer and less quotable than Carnegie and covers similar ground. Readers who found Carnegie manipulative sometimes prefer this one, which is more openly about self-interest and therefore less coy.