So many games have trophies these days anyway it's not real a problem :)
They have a nice feature too where you can keep a game you like for the price of a used game and they will send you the box for free ( you see the price once you have rented it). I actually did it once so far.
So if you rent something and actually like it a lot, you can keep it ( and you know you're not getting some scratched Blue Ray because it's the copy you have in your hands and have been playing)...