Good advice from everyone here, I would like to also add be sure the bow fits you, by that I mean what is the draw length of the bow and what is the draw length you need.
My draw length is 29in, I looked at a used bow that a co-worker had but the draw length was off, so I ordered a new bow, a PSE DIAMONDBACK, great bow. Also do you you know what your arrow cut length is, that is also important.
If you can find a good bow shop and ask them to help fit you to a bow, the bow you are thinking about buying may be just right for you.
I have seen alot of people buy a bow that does not fit them and then they loose interest in the sport when they cant shoot the bow very good.
A bow that is properly fitted to you will feel like a extension of your body and with practice you will be able to drill them big bucks with ease. You will find it to be a challenging and rewarding sport.
Also if you plan on hunting with it, you will get hooked, when I took my first buck with a bow I was forever hooked, nothing can compare to bow hunting, I like to rifle hunt but if given the chance I will bow hunt any time over rifle hunting, alot more rewarding experiance.