Find other local pinheads. That is the best advice you can have right now.

Pinball is almost full of great people... and a very small amount of bad apples. You will be able to spot the difference quickly.

So get to know some of the local chaps. Most of the people I know have or participate in informal gatherings or private leagues (private only because they are in peoples homes and most people can't handle 100 people showing up at their house). At its core, pinball is a social hobby. You get to know people as you chat with them week after week. When I come across a deal, if it is something I'm not interested in, I'll let one of my buddies know about it. They do the same for me. If the people you meet know you are looking, you increase your odds of finding a good machine at a reasonable price. One of them might even help you look at it for the first time or two so you know what to look for in a game.

Have fun with it. It is such a great hobby to be in.