What are one or three classic books in a certain field you know?

I am engaged in the sales industry. Let me tell you about three classic books I have read.

1, the secret of the transaction

This book can help you quickly open the customer's inner world and understand his real thoughts.

2, "sales and eloquence"

Salespeople rely on one mouth. This book teaches you what kind of speaking style can convince customers and be willing to pay the bill.

3, "interpersonal psychology"

Psychologist Napoleon said that success =85% interpersonal relationship+10% sales skill +5% opportunity, so it is very important to master good interpersonal relationship!