Many online music stores (as well as Amazon) include user reviews of gear they sell, and that’s certainly a place to start when you are considering a purchase. But also visit this one-stop site containing years of reviews, especially if you are considering buying a used item that is no longer sold new:
http://www.harmonycentral.com/
Since the review format is uniform and detailed, you may get more information than the frequent Amazon “I bought it 3 weeks ago – it’s awesome!”
Also see my post about determining a fair price for used gear if you missed it.