This definitely isn't just a Scotland thing... I grew up in Alabama and this was common there, and honestly I've seen this all over rural America. It's very common for farm stands during the harvesting season.

Still, cool website, I enjoyed a few articles there even if this one was very short.

When I was a preteen kid many years ago in Massachusetts enjoying the rural summer life, we used to go around to the local farms and beg produce off the farmers. We'd then set up a card table and a cash box at the side of the road somewhere and then go off to play for the day. While we were gone, the kindly wives of the farmers we'd gotten the produce from would come and buy back the produce from us for whatever minimal price we'd set on it. So as the afternoon wore on, we'd head back and excitedly collect our change and then head to the local general store to buy penny candy.

We didn't know at the time that it was the wives buying the produced back. We just thought we were amazingly successful shop keepers.

Yes, I've seen this in rural America. Purchased some firewood at a random stand on the highway. Pick some up, leave $5 in the box. Really nice to see this sort of thing in action.

Yup, there are quite a few little self-serve farm stands around here in Northern California.

And some firewood places like the ones the sibling commenter mentioned as well.

I've seen this in rural North Carolina. Eggs were available on-your-honor in the countryside back when the cities were out of eggs.