There are many things to be wary of such as ...
- Warped or swollen body
- Twisted neck
- Bad intonation
- Faulty electrics
Many sellers might be selling at guitar with a problem, but not even be aware of it themselves!
If possible, try and buy from listings with an actual video clip of the actual guitar you are bidding on being played.
(This is something I do for all the guitar listings I create). This is not easy to find, but at least this is the next best thing to
being able to inspect the guitar yourself.
Always buy from a reputable dealer. Whenever possible, if in your area, try and arrange a local inspection time.