I started in the late 70's. There were no obvious pin collectors and no way to communicate if there were any. I bought my first games, two EMs and a bowler only a couple of years old from a Government auction. One EM was missing the top glass. Both machines were working. The bowler needed some work, but it too was working with a small amount of help.
In the 80's I dealt with operators where they didn't want their machines to be put back on the street. Eventually I had to buy an operator out of all his pins -- maybe 80 machines. Many were Gottlieb system 1s that had perfect playfields and cabinets because of early failures. The Williams 40 pin connector and Bally nicad corrosion were problems.
The early 90s brought better focus, and more selectivity on my part.
Sales via the internet were possible through a video game forum before rgp became operational. The internet was a corporate operation and not yet public.
In the early 90s I bought a NIB F!4 off the loading dock heading for Germany for $700 and a BK2000 NIB for $1,200. The BK2000 was eventually sold to a former Williams pinball developer and remains in his possession.