“On” really is more casual/conversational than “nous”–I think both the original and your versions would seem stiff or impersonal coming from a shopkeeper in English, whereas the original French would not be confrontational in its word choice alone. Admittedly my reference point is modern conversational language in France and Switzerland, though.

https://www.commeunefrancaise.com/blog/on-or-nous#:~:text=%E....