You might want to contact Kraigwy about this. He will probably chime in shortly. He is a pretty straight shooter on what you should look for.
If I was looking for another, I would be looking for unusual burnishing or wear of the bolt. That seems to be an real good price and I would be curious why it is so cheap.
I suppose some fault could be well hidden and Kraigwy can really get you looking where you need to look.