When buying used power tools, test them first to see that they work and look closely at the power cord. If the cord is frayed or ripped or shows visible wiring underneath the plastic coating, it might not work properly.
While the overall quality of the power tool is important, a tool that is dirty or looks a little beat-up is not necessarily in bad condition. Consider the type of damage to the tool to decide if it can be cleaned up. Testing the tool is one of the most important aspects in choosing used tools. Ask the seller to plug it in to be sure it still runs.
When observing the power cords, also look to see if it is bent or the ground connector has broken off. Make sure it is fully attached to the power tool and is not starting to pull away from it. A loose connection could mean the tool won't last for much longer.