Years ago I bought an Offy intake at a thrift store for $6.99 and just bought it for... someday. I sat on it for more than 20 years thinking it was probably for a Pinto. But once I owned one it became obvious it was not for a Pinto. Turns out is is for a Vega and the last two sold on Ebay for over $100. I listed mine at $9.99 thinking it would draw interest, maybe a bidding war and I'd see just how far over the typical $100 selling price it would go. I mean, after all a $100 return on a $6.99 item isn't bad.
Well, the auction closed and having set no reserve it sold for - $9.99. After Ebay fees I might have made a dollar. Not the $90+ I was expecting. So, you never know.