I really don't, everything that I've sold I've collected over my many years of playing the game. It's much easier to sell when you
have everything.
As far as making a short run profit, you're on your own. You'd probably have to actually play the game
to measure what's going to be good when it drops, watch the various metas, keep up with the newest super-secret tech card so you can buy it low and sell it high. Good luck.
