From Webster's 1913:

Sell: To transfer to another for an equivalent; to give up for a valuable consideration; to dispose of in return for something, especially for money.

Selling, even for free, implies demand.

Implies, but doesn't prove.

https://www.nytimes.com/2019/11/21/books/donald-trump-jr-tri...

I was attempting to say that it's impossible to sell something that has zero demand.

i.e. you can't "sell" something when you can't even give it away.