I mean, flippers sometimes shake the trees and find games for sale that people generally never are able to find. So there's a positive.

On the other hand, my experience is they find these games, wipe the dirt off and say "shopped." Shame on me but I paid retail on a game from someone who upon reflection was a flipper, and it was listed as "completely reconditioned."

The pop bumper lighting wires were held down with hot glue
A lift ramp didn't work at all
Drop targets were the standard WD-40'd goopy slow drop
LED's were the standard cheap Chinese junk
The lockbar and coin door were spray painted silver.

AGAIN: SHAME ON ME, but this person added zero value to finding a game and I find this to be typical.

But, that's life I guess. It's encouraged to get that money, so that's what they're doing. Pinball buyers generally have money burning in their pocket, they're just taking advantage of the market.