what you are looking for is well known and trusted brands: Silverstone, Corsair, Pc Power and Cooling, OCZ, Antec do some fairly decent PSUs, Tagan do some good ones, but they also do some dreadful ones.
When you get a power supply, the +12V rail(s) are the most important ones to look out for. If there are multiple rails, add the amps and you get the total amps across the 12V rails
All internet buying has it's risk. If you are going to buy off of Ebay I would suggest setting up paypal. Ebay is pretty safe if you use paypal and make sure the person you are buying from has good feedback.
I have made over 100 purchases on ebay. only trouble i had was with my Ati 4850, which got lost in the postage system. my money got refunded because i used paypal, so paypal is a must.
If you look at the Charts you can see the 4850 will be better over 9600.
But it depends on your CPU. If you OC it youll increase your BUS between cpu and gpu thus getting better FPS. I would if i were you totaly forget the 9600 and go with 4850 or higher depending on your power supply