Yep, it would be stupid to try to sell a frame or whole bike on eBay or Craigslist (although some try). I've been thinking the same thing about my bike that was stolen. The frame probably got thrown in a dumpster and the part sold, over time, on eBay, craigslist, and local media.

I just bought a Cannondale frame as a replacement for the bike that was stolen. Is it stolen? I hope not. I'll check the serial numbers when I get it, but sometimes they are selling the stuff right back to the people whom they stole it from.