I know in Japan for instance, there’s a unmanned store where you can buy things with the only thing meeting you near the front entrance & exit is self checkout. It’s a trust based system where you walk in select what you want (without locking any essential or mundane item behind plexiglass), as in they depend on individuals having common sense on not stealing paying via a “honesty box” based on a honor system.
I don’t think there is any legal issue with it. Go take a drive out in the country and you will find farmers with a little stand outside where they put produce out for people to buy every day, and they leave a box got people to put cash into. (And just today, I saw one that took Venmo …)
The real issue might be that it would be impossible to get insurance in some places without an employee minding the store.