Re: fake emerald
Return it and report it to Ebay. If anything, he'll get fined by Nintendo itself for impersonating their merchandise.
Before buying anything, check for the Nintendo Seal. Also look at the box art closely-no matter how good a fake is, they always are bound to have a mistake. It might not be shiny, or it'll be off color...Perhaps it will have a misspelling.
Also, a good clue is if the cartridge isn't the right color (a red "Emerald" is a big clue XD). Always be careful when buying from Ebay, and if possible, I would try and get a receipt of sorts.
Good luck ^^