Definitely inspect it in person. Look at the boards in the backbox and look for anything that looks burned (molex connections). Look for battery acid leaking and any weird hacks (wires soldered directly to the board). Look under the playfield and look for anything that looks out of place (super-vague, I know..)

If you have ANY hesitations walk away! There are countless stories on here (myself included) who bought their first pin and had to deal with a boat load of issues. Seriously, if you have any hesitations walk away, there will be other pins that come along and the feeling of urgency is hard to overcome when buying your first pin. No matter what you buy be prepared to work on the pin, they are temperamental bastards! That being said, it is a great hobby and I am very glad I got into it. Good luck!

Good advice.