You get a few counterfeit bills from the casino and don't realize it until later when you get arrested. Can you get the money back from the casino assuming that the FBI believes your story.
If caught passing counterfeit bills and they believe it was unintentional you'll also have to sign a statement you passed the bills or you will be arrested. If it happens a second time it's prosecuted.
Not a good idea to hang around the cashiers cage any longer than is absolutely necessary, especially with a lot of Ben Franklins. I often have my wife cash in my chips.
I got a $100 bill from Casino A on the LV Strip and while buying in at Casino B across the street the dealer spotted it was a phony. I filled out the report with the Casino B and brought a copy of the report (and bill) to Casino A who again filled out a report and gave me $100 for my trouble.
I was going to ask the same question but it doesn't really matter because he knew where he got the fake bill. They aren't going to fight it because it's not worth it to them.