Did you contact the ffl dealer he was shipping it through to make sure they had it in their possession prior to sending payment? Unfortunately, there are a few scumbags on that site and those that say "for shipping only" and will not meet ftf, should never be contacted, as most of those are scams and they have fake items listed on many sites all over the place. It is a hard lesson to learn and I do feel for you. Like others have said, not much will really be done as it happens all the time. A friend of mine told me his grandmother was scammed out of almost $20K, as she fell for a kidnapping hoax just a couple weeks ago. Now she is getting solicited by scammers every day for other things. It is a shame we have so many scammers that can ruin things.
One thing you could do is log onto the FGT and start a couple ads exposing this guy, so others won't be tricked in the future. It doesn't do much for you but can help others.
Personally, I have had a few great transactions with some people on that site and have always required a ftf, they be a ccw holder, a phone number and a bill of sale for us both. Everyone I have done a transaction with had no problems with any of that.