Glad to hear you fixed it yourself
I'd suggest the flipper issue was coincidental. I don't think it would be a deliberate act.
However, I find it hard to understand the logic behind the game being "a dud" - but in the same breath suggest it be traded in to Bumper. Is the tech suggesting that Bumper refurbishes "duds" ? Who was he representing ? Himself, or Bumper ?
Anyway, glad to hear you saved yourself $150 by soldering a coil wire