Hi! Welcome to English 101.
Today, you get to learn that the phrase “selling” here means “recommending”.
It has nothing to do with literal transaction of goods or services for money. Instead, it is based on the concept of “salesmanship”, or convincing someone of the value of something - be it an idea or product. Recommending something is a method of selling it.
Fine, I’m not recommending anything. Perhaps someone else noticed this and commented "that’s not how you sell…