If you just sit and wait patiently and check your local Craigslist fairly often, you will definitely see a good variety of games in various conditions. Then if you're unsure, just consult here or IPDB for ratings and reviews, look over the rules and play field layout to see if you like it.
When you decide you want to try and buy one, here's what I generally try to look for.
To me, the most important thing is a good play field, preferably with no wear at all, with no raised or chipped inserts. This is all very difficult to fix unless you're skilled at that type of thing. And it can get costly to have it done. Also check all the mechanics, make sure all bumpers, switches, & etc. work. Run the tests in the game or just take the glass off and hit everything with your finger or drop the ball where it needs to go and make sure everything works. You'll want to get to know how much parts cost for the games you're planning on buying and how difficult they are to get, preferably before you go to test the game.
Next for me is cabinet. I don't want one all beat up, you can get decal kits for some games, and stencil kits for others, but a beat up cabinet to me is a few hundred to fix. Inspect all of the plastics. You may or may not find cracks or chips. Look at the back glass - if it's painted, is it holding up or flaking?
So if you know about what everything will cost to fix a game and bring it back to the high average retail price that game is getting, then you can try and negotiate with the seller a little bit better.
I just bought a $900 game for $300. The seller thought I was getting a great deal, but guess what - $300 back glass nowhere to be found, had to settle for a $200 remake. It needed board work. That was $200. It needed 2 score displays. Another $80. So now I'm into it for $780. Then I spent $100 on LED's and $20 on rubber. So now I'm into it for the $900 it would sell for in good condition. And I explained all the things I would need to do with my estimated costs to purchase the materials to the seller so they knew I wasn't just trying to hustle them. Time - plan on countless hours, because you'll love fine tuning and enhancing your machine. I don't do it for profit, I do it for the love of the game and so I can add them to my collection. But if I can come out ahead when I finally decide I want to sell any of my games, it will help me grow my collection and continue to do what I love a bit easier.
Being that you have engineering, soldering and schematic skills is a huge plus as you'll be able to fix virtually everything on your own. If you don't know the answer, you can usually find it here. I'm excited for you, good luck with your search and let us know what you end up with!