don't take any wooden nickels

To accept something that proves to be fraudulent or deceitful; to be swindled or conned. Primarily heard in US. I'm done accepting wooden nickels—capricious women who say they love me, then get bored and decide I'm not worth their time. My husband is a wonderful man, but he has about as much business sense as a grade-schooler. If I had let him accept all the wooden nickels offered flaky customers have tried to peddle on us, we'd have gone bankrupt years ago.

Take care and, specifically, try not to get swindled. The phrase is thought to have originated in the early 20th century when country residents visiting the city were considered easily duped. Primarily heard in US. Have fun tonight and don't take any wooden nickels!

Protect yourself (against fraud, loss, and so on). This warning against counterfeit coins dates from about 1900 and is distinctly American in origin, the nickel being a U.S. or Canadian five-cent coin. Why a wooden coin was selected is not known. Presumably making coins of wood would always have been more expensive than the intrinsic value of metal coins. Several writers suggest it replaced don’t take any wooden nutmegs, a now obsolete saying dating from colonial times when sharp traders sold wooden nutmegs mixed in with the real spice. In print the expression is found in Ring Lardner’s story, The Real Dope (1919), “In the mean wile—until we meet again—don’t take no wood nickles [sic] and don’t get impatient and be a good girlie.”

Don't let yourself be cheated. This expression was first heard in the early 20th century. Although there never were any wooden nickels as legal tender, country folk going to a city were likely to be cheated by all manner of ruses, including obviously counterfeit coins. Wooden nickels did exist, however, as bank promotions during and after the Great Depression; the “coins” were redeemable for prizes.