He pulls over and informs the vendor that it is fraud and false advertising to make absurd claims like this.
“No, no, no,” the vendor tells the cop, “my apples are a special variety. A scientific miracle. Buy just one seed, eat it, and you will notice an increase in intelligence. If not, I promise to refund your 20 dollars.”
“Alright,” says the cop. “But, if this doesn’t work, I’m shutting your operation down.” He hands over a 20 dollar bill, takes the seed, chews it up, and waits for it to kick in.
After a few moments, he says, “You know, even if you’re not lying, I could have bought a whole bag of your apples and had enough seeds to last me months.”
“Ah, yes!” says the vendor. “It’s working already!”