eBay is a viable income source. You just have to be on top of the market. My friend bought 15 copies of WoW and made about $300 on the deal. 13 of the 15 were sold to people in Brazil, where the game is not currently sold. Hence, they paid a premium for the game.
Also, woot.com and other discount sources continually sell items for 20-30% less than the eBay average. I've seen numerous items on woot that were $30-$90 cheaper than the -lowest- eBay auction. If you caught a few good woots a week/month, bought new games, new systems (read DS, PSP, ... PS3), you could definately make some money.