some people with farms near a road will have an unmanned produce stand with an honor box and they have been around for awhile. I think the higher the density the populace the more likely loss by theft gets to high. Likely there is some no matter where but it can be so low as to be virutally non existent. Even manned stores have loss from theft so it makes sense to do as long as the loss is below a point making it worth while. I actually wanted to get a multiflat in the city when I was younger that had a first floor storefront and do something like this.