if the computer "looked" cool, then it's probably worth poking around to see if he can get it running, how many prebuilts "look" cool...? not many, and the ones that do are the top of the line prebuilts, it's worth a shot in my opinion...
and seriously, y'all have never heard of dumpster diving...? people/retail stores throw away a lot of good stuff because they don't know how to fix it, and sometimes it's an easy fix, I personally don't "dumpster dive" but some people take that stuff seriously to the point where they have a schedule to which store dumps their trash and even when they do it (day of the week and time), though it is supposedly illegal to do outside of stores...