Fake Money Order: Is what I got a scam?

I put an ad on Craigs to sell a guitar, a guy contacted me asking if I would ship it if he sent a money order. We haggled the price down to $270 and he sent me a WalMart money order. I took it to a check cashing place and got my money... but I never felt safe sending the guitar! On one hand, he haggled, and the check cashing guy said it looked pretty legit to him. He has sent me many emails pleading for me to send the guitar, but I am scared. On the other hand, he says that he is leaving the US to go back to his country and needs the guitar asap to take back to his son. Foreigners and money orders sound fishy to me. I cashed the money order a month ago, and the clerk said they would come after me in two weeks if it didn't clear. How can I find out if it was a legit MO? I feel guilty taking the guy's money, but then again I feel foolish to think I might ship my guitar and then have the authorities after me if the MO was bad! How long does it take for check cashing places to contact you?