As a returning player from over a year ago I can safely say, the merchant situation is ridiculous. There really seems to be no way in telling what they will buy, even if they seem to have bought a lot of the items previously. I wasn't even looking for caps, just trying to get a few small guns instead of farming for a week trying to get my first craft skill so I can make an SMG. Everything I put in the window, I'm offered 0 caps.
Tried merchants in HUB, Klamath, NR, Redding, then finally NCR. I understand that it will be better when people can't sell the most random of things, but I'm trying to sell things like spiked knuckles, grenades, leather armor etc. On top of that you have people in guarded cities waiting in guarded merchant tents to steal, which makes a whole lot of sense. So after 2 days of trying to sell stuff, I was robbed in an instant and back to square one. I can live with that, the reason I play is because I enjoy risk vs reward, and hardcore based games. But at this point the reward is nothing, and the risk is everything.