Hey, don't forget the "miracle cow magnets" of the 70's that were to increase MPG by 30%.
There's a product that was once marketed directly to diesel truckers- it was basically an oil filter that operated by centrifugal force- the particulates were separated by the spin of this thing, which was powered by the engine. (I'm going from memory here...)
It was presented to a lot of folks, and it was mostly laughed at- much like the mouthbreathers who have chimed in here. Eventually, though, Mack picked up the idea, and it's now parrt of the standard design of their engines.
If my facts are wrong, please correct me- it's been years since I heard that story.
I just mention that to say- not everything is a scam, and not everyone is a ripoff artist.