You know the previous owner of a bike was a bad owner when...
You know the previous owner of a bike you are considering buying didn't know what he was doing when:
All the spokes were tensioned apparently with pliers... there is no purchase on any spokes for a spoke wrench, as it has been rounded out.
The frame has holes drilled in it to install rivnuts for various accesseries... and the frame is (or more exactly was) OCLV carbon fiber.
(Thankfully I didn't see any of the above occuring during my browsing for a commute bike, but the thought came to mind when someone I know asked about why people bother with spoke wrenches when pliers work as well...)