The first thing I do when I encounter any expensive game is looking for serial numbers. For Nintendo 64 games look in the cartridge slot. On authentic games, if you look in the groves of the N64 game you see some numbering in the slots. 

Recently we obtained a box of some really Rare Super Nintendo titles.  At first glance it was pretty obvious to tell these games where not authentic.  Below are points about how to spot these fake/ counterfeit "reproduction" SNES Games.