$1 Error Coin

Definitely not a mint error. This is what is known as a "vise job". You can make as many as you wish, just by squeezing two (or more) coins together in a vise.

It's also known as a "vise job", partly because that's how Americans spell "vise", and partly because only a fraudulent person would hype one up for sale on ebay. In this case, the seller clearly has no idea what a "mule error" actually is, or should look like.

It's possible that such a mutilation occurs "naturally", if for example a stack of coins were used to level off a piece of heavy furniture for a long time. But far more often, it's just someone fooling around in their workshop.

according to the seller it was found in circulation.

To manufacture this "mule" would likely be using an industrial hydraulic press with a 10c coin pressed into the $1 coin at high pressure with hardwood on the bottom to protect the unaltered side which would explain the flex resulting in a curvature

Such presses are in most engineering workshops and this seller should be made aware that defacing currency is a criminal offence

http://www.ramint.gov.au/designs/ra...ns/using.cfm