The most useful book I've ever read was Dale Carnegie's "How to win friends and influence people."
en.wikipedia.org
Implementing the techniques in this book many years ago, I talked my way into a FREE transmission repair at Aamco.
Those things are expensive!
Details: I paid them to rebuild my mustangs transmission 18 months earlier - with a 12 month warranty - I was 6 months beyond their obligations and they wanted to charge me. I asked to speak with the manager, got the owner, and charmed my way into a free repair practically quoting some of the more charming parts of this book , parading as my own organic dialogue.

How to Win Friends and Influence People - Wikipedia
Implementing the techniques in this book many years ago, I talked my way into a FREE transmission repair at Aamco.
Those things are expensive!
Details: I paid them to rebuild my mustangs transmission 18 months earlier - with a 12 month warranty - I was 6 months beyond their obligations and they wanted to charge me. I asked to speak with the manager, got the owner, and charmed my way into a free repair practically quoting some of the more charming parts of this book , parading as my own organic dialogue.