Agreed that going through the lamp, switch and solonoids tests is a must. Same with checking out the boards.

After that, playing.it.will give you the best feel. Is the playfield warped, are the flippers strong, etc? You'll have to play to know.

Check the holes (database, skull, above the pops) for wear. Make sure balls hit into them don't rebound out due to wear. Especially check the one behind the skull and make sure balls hit into the skull settle into the hole QUICKLY and the drop target pops back up to block additional balls from entering during multi-ball. Otherwise, you are asking for trouble.

Make sure cannon fires correctly, and is dialed in so that it actually fires whenever you pull the trigger when it is pointed at ALL of the 5 bank targets.

Pay attention to the skill shot and make sure the gun/plunger consistently hits the same target every time.you fire it.

Check for wear around the pop bumper skirts. Very common in T2.

Check for broken plastics. Lots of air balls in this game if not set right or coil sizes are wrong.

Check right (plastic) ramp to make sure it isn't broken or cracked.

Listen to DMD and make sure it isn't buzzing/making noticable noise. If it is, it'll need to be replaced.

Lift playfield and look over the bottomside. Any noticable hacks?

Look at the bottom inside of the cabinet. Run you finger over it. How dirty is it? If your finger comes back full black, it probably hasn't been cleaned well In a while.

Good Luck!