I fellow club member just had the same luck - sold a Raptor 30 rx ready for $50 to some kid (I used to own this, just the blades were worth more).
Kid showed up with the dad, seemed to be really interested in rc flying, but didn't have much money so he felt sorry and gave him a good deal...
2 weeks later the helicopter and some other rc items show up on Craigslist, asking for more then the 'new' price.
These people ruin it for others. I always sell used stuff for little money to people I know