Hi dyret, and welcome to SaleHoo
You're talking about a very competitive market, and some of those prices you see on ebay reflect sellers that are spending a lot of money on stock from distributors to get high volume discounts, then selling with a very low margin to compete.
It's a pretty regular business model you see used to sell effectively on ebay these days, but this market I have first hand knowledge of as it's a field that I myself am now involved in.
I can tell you that it is possible to get into the market, and I believe make quite good money over time, but you need to spend time making the right contacts within the industry, and spend quite a bit of cash on stock to get yourself in at the right end.
If you don't have the time to really dedicate to it, and the budget to allow you to throw some serious money at building up a stock profile, then it's probably not the best choice of business to chase.
One tip, if you do chase after it I would suggest you don't limit yourself to just PS3 games, for example at the moment Wii holds the top few spots in the top ten games sold, so you would be limiting your market to only go after PS3.