Make sure the pf moves smoothly up and down through all 3 positions.
Make sure the upper flipper can cleanly shoot the ramp.
Make sure all 5 dalek armor targets / optos are working.
Make sure the display is crisp and clear, no missing lines or columns, no degassing in progress.
Make sure the boards have no weird hacks.
Make sure there is no corrosion damage to the mpu. Even slight corrosion can make the mpu break down.
Make sure battery holder is removed from mpu and either placed remotely, or replaced with nvram.
Do a switch test to make sure all switches activate correctly, and a solenoid test too.
Play some games and hit both flippers at the same time a bunch to test for the Williams reset issue, if the game has it then the power board will need new caps, rectifiers, and lm323. If the game has a little daughter board between the power board and you, then it probably has the issue but it's being corrected by the daughter board. In that case it will need a power board restore soon.
Warning. Keep hands away from mini play field.
Congrats, awesome game, a long term keeper!