They're showing up more and more frequently on the site Craig's List.
The first posts were seen in May and exploded over the summer.
Demand has apparently been big for those who are selling the tests.
The tests are going for about $25.
Whether they're being used as a prank or something else, the fake results could open up the buyer to legal drama.
"There's civil liability, and there could be criminal liability as well," said legal analyst Paul Henderson. "That person that's selling the test, if they are participating as part of that scam, then they would be liable as well."
Those caught using the tests in a fraudulent matter are not likely to go to jail, but could be sued.