Several years ago, a man sold a Banksy work of art for just $175.
He did it because he didn't realize what a Banksy work of art is actually worth.
In fairness, the buyer apparently told the seller his graffiti-covered door was actually a work by the esteemed, mysterious artist Banksy, but the seller didn't appear to understand the monetary implications of that fact.
You may be familiar with the Latin translation of Caveat Emptor: "Let the buyer beware".
But the flip side of that coin is equally important.
Scito quid est quod vendis
In English, that would be, "know what you sell."
It may not be as catchy as caveat emptor, but it's clearly just as important.