Lotso bandwidth spent on discussing pros and cons of various scope manufacturers. How about some advice for those of us who have narrowed our choices, and are at the gunshow looking for a good deal on a used unit. How can we tell if we're looking at someone else's problem? What do we look for as signs of defects? What tests can we put the unit through? What are the tell-tale signs of a unit that might look good on the outside, but has performance, er um, functional issues?