stolen credit cards
I use steamtrades.com. I simply trade key for key. Those won't be charged back because people have been holding them for a while. They would have had been disabled by the time they're traded. I mostly just trade bundle games for other bundle games.
I use Steamtrades too for the same reason. I stopped using it but might return. Especially if I upgraded my PC.
Nice, bundle leftovers are safe for sure. That's where key trading is beneficial for all parties involved.