What is the difference between direct selling and direct marketing?

If I went into a classroom where you were having a lesson, interrupted you and your professor and asked him to try my massage tool for growing his hair (this happened to me), this would be direct selling.

You would secretly laugh at your professor while he massaged his bold head.

Your professor is a polite man so he wouldn’t say anything.

If answered 543 questions on Quora about tools and ways to grow hair on a bold head by helping people make better decisions about such an important part of their body.

At the end of each answer I would use a short link to my free mini course I send them by email for 10 days about various methods of growing hair.

At the end of the mini course I would offer them my special hair massage tool (which you watched me try on your polite professor).

This would be direct marketing.

Direct selling is useless and annoying.

​Direct marketing is priceless.