I’m not talking about “laundered” money. We’ve had this problem a number of times when exchanging currency in other countries. If there is any writing on a bill, or if it’s torn, or even if it just looks crumpled up, foreign banks and moneychangers won’t accept it. Most money exchange businesses insist on clean, crisp bills, even with smaller denominations. They will also not accept older currency, especially older $100 and $20 bills with the smaller portrait image of Ben and Andy.
So before you go overseas, inspect the money you’re bringing to make sure it will be accepted. Most cash dispensed from ATMs is acceptable. Better yet, you can go to your bank and ask for new bills.