This is a long shot.....
See if you can file a small claims court action. I forget if you said you had his name or not, but you might be able to start the claim even if you don't know his address. Put down "no fixed address" or something. In anycase, once you have the claim registered, then go to the Apple Store. With proper court document in hand, you may find that the scammer's address is now available to you.
If you can wrinkle out the address this way, you now have two options.
1) Serve him with papers. If he shows up, since you have serial number, and his address, and a copy of the Craigslist listing, and all the email correspondence you had, and he will only have a wild and colourful story, you will likely win. In civil case, which this is, the judge only needs to find "on balance" - not "beyond a reasonable doubt". In a civil case, having a file full of papers beats a wild and colourful story. If you win, the scammer will need to pay the $300 plus all the court costs. He will likely not pay, and you're screwed unless you can find his bank and garnishee it.
Talk to the court clerk, and get their advice.
2) Find his scam on Craigslist (use a different email since he is likely smart enough to not respond to a previous victim) and meet him again - with a friend nearby. When he shows you the working Mini.... serve him with papers, and take the Mini. Have a bill of sale all ready to go. Tell him, sign over the Mini to (you need this so he then doesn't claim you stole it) and you'll drop the court-case. Hopefully he doesn't want to deal with paperwork, and he'll sign.
For the scammer, it will be easier to just steal another Mini and continue his scam than to get bogged down in paperwork.
If you can, find a detective who is sympathetic and give them copies of the Craiglist, his name and address. Perhaps they will sting him.
Good Luck.
That is sad that people go around and take advantage of others like this. 
