Likes: Counter offers - much better than flat declines.
I really like trading with people who are willing to negotiate - I find that we can almost always work out a deal. We all value certain games differently, but I prefer to use ebay completed listings, as "sell" prices are a much more accurate way to valuate a game than "list" prices are. I also include shipping when calculating this amount, as there is no reason a "free shipping" listing should count more than one with an inflated shipping charge. The condition of the game also factors in.
Sure, www.videogamepricecharts.com is a helpful tool, but not for matching the value of trades because they take into account a bunch of different metrics - only one of which is actually what the games have been selling for (and even that one is seriously flawed because it doesn't include shipping, so "free shipping" listings show up as more valuable. It also lumps all conditions of the game together, whether it is damaged, full package, or sealed, and even video game lots that include the game you are pricing are included for the value of the individual game). I understand that different people may valuate games differently than I do, but quoting prices like that is pretty disingenuous.
And if you tell me you can get a game for $0.01 on Amazon we are probably done negotiating, because the $4 shipping charge has been *conveniently* overlooked. But show me where you can get a game shipped to you for $0.01 and I will price match :)