It appears that the buyer didn't consider that they bought a stolen MBP. My first guess after reading this is that the real owner discovered their computer was

It appears that the buyer didn't consider that they bought a stolen MBP. My first guess after reading this is that the real owner discovered their computer was stolen. This is a good reason to test and change the iCloud account while the seller is standing there. I am not sure about the laptops, but an iPad/iPhone needs the same pin to change the account it is associated with, so you get some immediate evidence if you are buying something stolen.