My dad sold a guitar on Craigslist.com, does this look like he may get scammed?

That's a scam. Wait for the check to clear before you send the guitar (but I can guarantee that it won't clear). I work at a bank and this goes on a lot with on-line auctions. You'll probably need to report it to the proper authorities. People usually don't "accidentally" over pay, not by that much anyways.