Can you tell us what happened with this? I bought a used 2011 Macbook Pro and the machine was locked remotely later that night. When I contacted the seller, I was directed to another person on craigslist that claimed to be able to unlock the machine for $200. It looked like a scam, so I passed.
I checked out the serial number with Apple and the local police before I bought the machine. I even took my Sprint wireless device and booted off of my firewire disk to check Internet access. Nothing seemed strange and the guy was very relaxed. Now, the number from craigslist is no longer working after I told him I reported the matter to the police and wanted my money back. It was one of those burner numbers registered with a fake name. These guys are pros. The police are unwilling to spend time on a small crime like this.
Did Apple return the machine to you with the firmware password removed? Did they charge for the service? I would hate to lose the $750 I paid for the machine.