I suggest you post this on the "Ask A Mechanic" section. Better still, take the table mechanic with you that you want to use to break down, move and re-assemble the table. If you don't already have one picked out again you can ask on that section who's available in your area.
I'm not a mechanic myself but here's some quick suggestions from my own experience:
If the table is still assembled play the're a standard three rail shot to test the speed of the cushions you should try. (Shoot from the first diamond on the long rail at one end, aim at second diamond from the opposite corner long rail and the ball should bank into the corner pocket.) If it banks long or short adjust your aim point on the rail to determine the cushion speed. Then move down to the other end and shoot from their to test the all six cushions. Hit the shot pretty hard and listen for dull thuds or thumps.
However the rail rubber is easily replaced if bad, and you might want to do this anyway to improve the pockets. (Both to make them tighter and more consistent by extending the sub rails.)
Also of concern on a used table would be the slate and frame. If the table is disassembled make sure to check the condition of the slate and frame visually.
Also on a GC look at the pockets, are they mounted correctly with machine bolts or held on with nails?