Flimflam

It was a wretched theory. They postulated that
if we’d all collaborate, we’d lose all our fat.
They weren’t very subtle. They gave us tubes of stuff
to squeeze over the food we ate, but never quite enough.
We had to buy the second batch, and prices just kept rising.
Whereas we never lost a pound—a result not surprising.
Later, they skipped out of town—an act our friends found funny.
They told us from the first the only thing we’d lose is money!!!

Prompt words today are wretch, subtle, collaborate, postulate and tube.