flyEYE
there was a batch of ver. 2.1 flight control boards that had issues with how the gyros were mounted. here's a link to the discussion on the german forum where the "flip of death" issue is finally attributed to faulty gyro mounting.
http://forum.mikrokopter.de/topic-18336-8.html
you'll have to read a page or two before to get a better understanding but it would be worth it to understand the problem they're pointing out so you can see if the hexa you're looking at has the same issue.
if the fc board isn't ver 2.1 then you don't have to worry about it.
as for the rest of it, look at the construction of the boards for sound solder joints. were the boards built by the guy you're buying it from or did he buy them pre-assembled from a dealer?
will the weather be good enough to see him fly it for you? i wouldn't buy anything if i didn't have an opportunity to see if fly for a reasonable amount of time.
the older boards have limitations as to what versions of the software they can support and the older BL (brushless motor controllers, they're called ESC's everywhere else) boards have a lower current limit than the newer 2.0 version. if dennyR reads this maybe he can contribute to that point as he's done a lot of bench testing with various prop/battery combos and he's familiar with what the BL's can handle.
in general, look for neat assembly of the boards, wires, frame, etc and look for any evidence of crashes like broken board corners where the mounting holes are. a neat assembly should give some credibility to the construction of the boards if he did the solder work.
that's all i have. maybe someone else will add to it. good luck!
bart
