My experience has been that most end up in the route guys old dilapidated pole barn/warehouse where the roof leaks and they have no intention on selling unless they get that "ebay price" for them. Granted they're comparing their neglected, needing work, routed machine to some guys fully restored model on ebay and think you're lowballing them when you factor in costs like playfield touch-up, rebuilding boards, purchasing new pieces to fix the broken stuff.
One local guy does a fall cleaning around this time of year. His collection is mostly older arcade games. I usually see a busted up pile of waterlogged cabinets sitting outside of his warehouse. He takes the electrical components off to the dump.