We had a washing machine or two like that in college as well. You could push the tray in and out fast enough that the coins wouldn’t drop or something like that. It didn’t always work but worked often enough to perhaps halve my cost.
There was also a soda machine where you could set the coin on the edge of the slot, sort of shoot it in by flicking your finger down and it would register but then drop out the coin return. Was a skill to it and, again, didn’t always work but I got plenty of free pop that way.