What are your top tips for buying 2nd hand guitars. i.e, how to spot an ebay lemon or how to examine guitars before parting with your cash?
There should be a sticky on this somewhere really, it'd be pretty useful I think.

Tanglewood TW28STR
PRS Soapbar SE II
Epiphone LP100

Roland Cube 30x (New!)
The neck is the most flawed of course.

Compare the shape and height of the last fret (since it gets used so little) to the first five cause they get the most action usually. A refret is expensive!

Go up every string on every fret to find any dead spots or fretting out, it's the best way to tell if a neck needs work.

Make some whole step bends past the 12th fret to find any fretting out also.
Make sure the neck is not excessively bowed in either direction.

Check the neck for any cracks, especially near the headstock and behind locking nuts where they get a lot of abuse.

Make sure all the controls work for their intended purpose without noises.

Check for stress cracks in the body near the neck where they join.

That's all I can think of at the moment.