In the mid 70's I hired a green kid as a "gopher". We sent him to the local speed shop for checkered paint in a spray bomb and not to let the guys there to try and sell him any bigger sizes. Phoned my buddy at the speed shop and told him the story and told him to play along and that he only had it in gallon cans.
The poor kid got mad at the speed shop owner and told him that he expected him to be an ***hole because his boss (me) told him this would happen and he demanded the spray bomb.
How about "sky hooks" for pulling engines outside?
Told my sister-in law many years ago that cream hardner for body filler would help clear up her acne because it contained peroxide. She was willing to try it but I would't let her.
Cam shafts made of a special rubber so that when the engine revs up the cam starts stretching and expanding to give you more lift. Brother in law looked for weeks to buy one.
There's got to be a lot more I've tried to pull off, I'll keep on thinking.