I agree. I've also long held a different but complementary view: that all establishments should (hopefully, out of the goodness of their hearts) put up signs that basically say, "this is how it works here".

(For example, at a grocery store in the US, the sign would say something like, "This store sells the items you see inside that have a price label by them. To buy something, take it with you to one of the numbered short aisles [registers] toward the exit and place it on the belt. If you need many items, you may want to use one of the baskets or carts provided near this sign. The store employee at the register will tell you how much the item costs, and you can pay with ...")

While most of it would be obvious to everyone and something parents automatically teach, everyone might find some different part of it to be novel. And I suspect that this easily-correctible "double illusion of transparency", in which people don't think such signs would convey anything new, prevents a lot of beneficial activity from happening.