Once you cycle through each villager buying something, just save and quit, then reload.
They will buy all day.
I do this with expensive fruit.
Like apples, perfect peaches etc. BUT.. I'm not sure how many people know this, but only stack 5 of the expensive fruits, and charge the maximum -> 9999.
You can't go higher than that.
With less expensive fruit, have them in stacks of nine.
They will pay 8000 for them.
It's quite profitable!