I started in the early 80's helping my friend and his dad with a small route. They taught me how to clean & rebuild score reels, stepper units, etc. Schematics? HA! They usually where nowhere to be found. Just keep cleaning and adjusting until it works! They had a half-dozen Puck & Ball Bowlers to add to the fun. There were buckets of parts that came from games that got smashed up, because that's just how they did it. Why sell a pinball to someone for their home when they'd just hound you for repairs?
Then we got a Gorgar for $200, and Flash Gordon was cheap too. NOW we needed the books. I don't know how we kept them running, but the Distributor always seemed to have someone who knew what he was talking about that we could ask. We'd add a pinball to the route occasionally as they came up, and did a lot of video game conversions. The main money was in Jukes & pool. I don't miss doing AMI juke mech adjustments late on Friday night in a packed bar!
I heard about Pinball Expo somehow in early '88. Missed that year, but made it to the one in '89. Police Force & EATPM were the latest, and Bone Busters was the Tourney Game. Data East had Monday Night Football out, but I don't think they were there. Pinball Resource and other vendors were there though, and that was a big help in getting parts. Tim Arnold would make it to those early Expos and was always interesting to talk to.
I subscribed to Pinball Trader, and that kept us in touch with other collectors, vendors and other shows. Calling Steve Young was the only way to do it in those days. Russ Jensen, Sam Harvey and all the other old-timers were always willing to help out with any questions, but you'd have to call them, send them a letter or wait until Expo.
Pingame Journal started up, and The Pinball Trader got bought by Gameroom. It wasn't until the Internet that the hobby took off and is what it is today.
And it's no kidding, In the late '90's, WPC games were everywhere for way under $2000.