Many of the mistakes that make coins worth more than their face value are tiny errors that you might need a magnifying glass to see or you'll never notice them. Things like letters being too close together or a small extra line can make the currency pretty valuable, but on one quarter, there is a common mistake that you will definitely see.
The Coinhubs Instagram account pointed it out, calling it the "funniest minting error ever." It's on some 2007 Wyoming state quarters. You want to look for ones that have a small letter P on the heads side, under where it says "In God We Trust." On the tails side, typically it shows a bucking bronco with a rider, but on the quarters with the mistake, the horse is doing more than just bucking. If you look at its butt, due to a mint error, it seems as if the horse is pooping.
If you have a quarter with the mistake, it is worth at least $25, but if it is in perfect condition, it can sell for as much as $2,000. As to where you can get paid for the coin, you can try a pawn shop but they won't give you top dollar, so you might be better off selling on eBay or in a Facebook group for coin collectors.
And if you find yourself digging through your couch cushions or rummaging through your coin jars, be sure to keep an eye out for some other coins that might have value!