Is this machine supposed to be working?
If so, seller should have it set up and plugged in so you can really check it out.
You should be able to take the glass off and verify that all pop bumpers, slingshots, and switches/targets/rollovers are working.
Should be able to start up a 4-player game and verify scoring displays working.
It's always good to look at the back side of the backglass to see if artwork is flaking/peeling off in spots.
Does the bottom and/or back of the cabinet look nice, or is it rotted & moldy?
Concerning the road trip, you may want to have a back-up plan of a few interesting places to stop and check-out on the way there or back, if you have time, and are not coming home with a machine. Then it may not feel like a wasted trip if you decide to pass on the machine.
Let us know later how it all works out.