I recently found a site selling games called jjgames.com. Most of their limited inventory of used games is fairly cheap but a few of their games are outragous when you consider according to the database here that they are fairly common.
Case in point, Back to the future 3 for the sega genesis cart only is going for 110 dollars. Worms armageddon for the n64 cart only 164 dollars; and Super monkeyball for the x-box is going for 184 dollars.
Anyone have any ideas as to why the ridiculous prices for these games in particular?