I almost accidentally did a sideline deal once at a local mom&pop shop. I was in on my lunchbreak, and some guy brings in Xenosaga & some other PSOne RPG (it's been several years, can't remember what) to trade in. I saw them & the condition they were in and expressed my interest. My intention was to make sure the guy who owns the place knew I wanted them - I had been going to his place for years. But the guy who was trading saw my interest and offered them straight to me. I told the guy running the store it was not my intention to cut him out of the deal, but he said he didn't mind since he knew us both & we were both good customers. As it turned out, I didn't have any cash on me anyway and there was no nearby ATM, so I left. When I got back to work I called to see if he had traded them in anyway, and he did. Asked the guy to hold them for me, and bought them after work. Felt MUCH better about it to.
What people fail to realize is that these stores spend money on rent, advertising, utilites, salary, etc. It's because of all this money they spend that ppl come in in the first place to sell them games. You walking in off the street not only don't have this overhead, but you're taking advantage of the money the store is spending to draw the trader out in the first place. Do I think Gamestop/EB offers good money for trade-ins? No, not unless they're running a special, which is why I don't trade them games. But does that give me the right to take advantage of their resources for my personal gain? No, it doesn't. Justify it all you want, it's still wrong.