To be more exact, rob the rich to make themselves (shop owners) even richer! Do you think the shop owners are poor people?? Or do they donate those price differences to the poor like robin hood? I don't think so. :) Thus they are not Robin Hood but they just try to take advantage to make themselves richer, simple as that. They also know if they charge as high to the poorer people then they cannot make the sale, and hence no profit to their pockets too! It's all just simply business, nothing more really. That method is a discriminative pricing. Btw such method can backfire as well since some richer people also dress down to look humble.
But it is the car that is changing tyres, not the owner, so he dress humble, but car still BMW.....hahahahahha