I agree that is a very annoying scam when this happens. It is definitely not money laundering. The buyer gets cash and you are left with a fake check or money order.
The key characteristic is that they overpay and ask you to wire the change to a local person who will arrange for shipping. But the wire transfer can be claimed anywhere and is typically redeemed in a third world country. This type of scam works best for high value hard to transport items like boats, cars, or horses. Your bank has 60 or 90 days to come back to you when the check is fraudulent. It is not enough to say the check cleared.
My local bank has a notice warning customers not to cash checks for unknown third parties who will get a portion of the check in return.