Usually, when something has a mistake on it, it isn't worth much and might even take away from the thing's value - you'd probably ask for a refund if a word was misspelled in a tattoo - but that's not always how it is with errors and some mistakes make items way more valuable. Such is the case for coins. Misprinted money can be worth tons and can turn a penny from being worth one cent to $100,000.
There are many coins out there that are worth more than face value and one to be on the lookout for is a unique Georgia state quarter. The coin was minted in 1999 when the Treasury first began the state quarters program. At the same time, the Mint was working on a new metal alloy for coins, one with a gold tint to it that was eventually used for the one dollar Sacagawea coins that came out in 2000. Curious how the alloy would look on quarters, a bunch of Georgia state ones were minted using it. The Treasury decided not to go with the alloy on quarters, but the ones minted with it were still released and are now very much desired by collectors. In fact, one just sold for $7,200.
So if you get change and one of the quarters looks more golden than you are used to, you might have something worth a whole lot more than 25 cents. Of course, that's not the only quarter with a mistake on it, and some of those errors can be pretty funny/gross.
As for what to do if you ever find a coin with a mistake on it, the easiest way to sell it is by listing it on eBay.