Appreciate it may look rough cosmetically in that price range. What am i looking for operational wise, magnet working, motor working? Fire it up and try it under load somehow?
Yes, if you can test it, great. There are two magnets in the base, one common fault is for one of the magnets to fail. Stick it to something pretty heavy and try to push it over. IIRC on 25mm plate they have 250kg of 'clamping force'. Easy enough to try. If the magnet has gone its a scrapper.
Try drilling a hole, and as long as it doesnt sound rough or stall you might be onto a winner.