I generally steer clear of 2nd hand electronic products unless advertised as brand new or as new...wherever possible if the seller is in same state you can inspect b4 purchasing.
I've bought heaps of 2nd hand parts online or through importers eg: catback exhausts, wheels, misc parts....
You just need to find a reputable seller and someone that can accurately describe the condition of the 2nd hand product you are buying. As always, there is an element of risk on the buyers end....but if everything is as described and you are happy with it, at the end of the day you save heaps off retail prices...
My 2c..