Yeah but then using a barter system is probably outlawed in those societies, which would have a chilling effect because you don't know if someone is safe to ask

Yeah but then using a barter system is probably outlawed in those societies, which would have a chilling effect because you don't know if someone is safe to ask about the alternative method for fear of being reported. A casual interaction between shopkeeper and customer would never be facilitated by barter in such a hostile environment.