I'm not saying eBay is all bad, I've had plenty of great experiences with their service- but Pokemon games are notoriously bootlegged. The guy that i bought them from had legit pictures posted and a rating of 1,000+. Upon opening the games, only 2 things were suspicious:
1) The carts for Ruby and Fire were the same type of plastic (In reality, Fire is more of a solid red-orange, while ruby is a dark red with glitter mixed in the plastic). I didn't know there was a difference, since I had never owned/seen the games prior to purchase. Upon further inspections, the serial numbers stamped in the backs of all the carts were the same.
2) The instruction manuals- the paper was very thin, and none of the 5 games came with myNintendo registration cards.
Luckly I was able to get eBay and Paypal to support me, and I got a refund, but it still sucked.