And the Hamiltons, Jacksons and Grants, too. Subconsciously, we think old, grimy-looking bills are worth less than clean, crisp ones. And so...we generally spend them faster and more freely, found a study published in the Journal of Consumer Research. Luckily, there's a simple solution: If possible, ask for newer bills when getting cash back.
Bonus: Paying with clean bills might get you a better deal: A field study at a farmers market found that sellers more frequently overcharged customers after touching grubby banknotes than new ones.