While the situations you cite are relatively less common, I don't think the social norm in those situations is at all unclear. Walking through the back storage

While the situations you cite are relatively less common, I don't think the social norm in those situations is at all unclear. Walking through the back storage room to find the restroom after asking is fine, but doing so without asking isn't nor using is your bathroom trip to rifle through merchandise. I think it's only us nerds with our low social sensitivity and literal minded-ness would think otherwise.