Arilau: you should read a bit and make sure you do not expose yourself - even when you trust that person and you are convinced there is nothing wrong with that money - that transaction will be flagged:
I'm not an expert at all, but have had international assignments on my job and know that there are rules that you have to follow and transactions you should avoid. This would be similar to you accepting to take with you someone else's luggage in a plane.
You should also know that it takes a long time for a foreign check to actually clear. You can cash the check and your bank will (may) give you the money after a few days, and then come back weeks later if/when the check ultimately bounces and you would have to repay the bank. FWIW