He knocks at a young man's apartment and asks him, “Would you like to buy a top-of-the-line toothbrush? It's only ten dollars.”
“Ten bucks for a toothbrush!” the man yells
“What moron would pay ten dollars for a toothbrush? You're out of your mind.”
“All right then,” the salesman continues, “then how about a fresh-baked brownie for a dollar?” The man thinks it over and says, “Okay, why not?”
The salesman hands over the brownie
The man takes a bite and spits it out onto the floor in the hallway.
“My god, that tastes like crap!” he yells.
“Well, that's because it is crap,” the salesman explains
“So can I interest you in a toothbrush?”