So with me knowing about ze "horrors of Gamestop" I'm trying find alternative methods to selling/trading in my games.

So how reliable is Amazon trade-ins? I know that I'll generally get a better deal and all (I checked each game I have yeah they give around 15% more), but how complicated is it to ship the game, are there problems receiving credit etc.?

I havent traded game sin, but Amazon is a stellar company in every regard that I have dealt with them. I wouldn't worry.

amazon's the best business I've traded into. They give better prices, and their prices fluctuate. So you can make trade in order, watch for a couple days and see if it goes up. It has free shipping. It's really easy, you just print a a packing slip. Package it, and then tape prepaid label, you don't have to paypal or anything. If for any reason they don't like the quality of your game, they'll send it back for free.

You only get amazon credit. 

Ebay will get you the most money. But it's a pain in the butt, dealing with feedback, users doing shady things, etc.

What kind of games you selling?

instead of trading in, i would just sell them yourself. U get more money that way! I would join PSN + when u get a free game, then sell ur original.