Buyers will always have different experiences even if you sold the exact same pin to 10 different buyers.
I might buy it and find several small faults and simply fix them - and be happy.
Another buyer (maybe with little or no electronic or mechanical/handyman skills) might be horrified with the discovery of a few small things and throw his hands in the air and scream "I've been robbed"
The simple facts are:
(1) a pinball machine is a fairly complex piece of electronic & mechanical engineering made DOWN to a price
(2) most of the complaints are coming from sales of machines that are 20~30 years old
Seriously - what does a buyer expect???? Too much I suspect.