A few weeks ago a guy got scammed out of $1000 on the LF forum when a guy appeared asking questions about a very rare soft focus lens, with a lot of red flags. The "seller" even asked the buyer to split the postal money orders into two different checks, "in case the post office doesn't have enough money."
I always ask for a phone number, name, and address on CL sales. Then I do some snooping and make sure everything matches up. Then I talk to the seller on the phone, asking questions only someone holding the camera could answer. I've even asked for a picture be taken with a special item (a coin) in it. You have to do all you can to avoid ripoffs when sending large amounts of money to total strangers.
If you have talked to him, and his name matches his address and phone, you're probably ok. If not, you better talk to the PO fast about cancelling the money order, if it's even possible.