A friend of mine was approached when he tried to sell his flat-bottom race boat. Offer from Spain, legit looking money order came, for an amount greater than the asking price. He went to deposit the money order and the teller decided to call the bank it was issued from.... it was not legit.
The scammer was seeking to have the friend "forward" the "excess" funds to a 3rd party.
He was very lucky. I've heard that some of these scams start with a legitimate cashier's check, on a foreign bank of course. They copy the check or make a forgery so the check has a bank number which will seem to be good. A call to the bank will probably get an OK for the check. They can do this several times before they take the original (good) cashier's check back to the bank along with all of the suckers' checks for deposit or cash.