I remember reading an article about a guy who wanted to make a point about the antiques world, and made a copy of a very desired and rare old chair. He sold it for next to nothing to an antiques dealer without making any claims as to what it was or wasn't. Somebody thinking they'd found a steal bought it from the dealer and sold it on for a big profit. It eventually ended up at a museum, at which point the original maker approached them and told them it wasn't what they thought it was. They told him they were experts and could vouch for its authenticity, until he told them to x-ray it and they'd see modern screws hidden in it. Oops.