I was at M+S, in the clothing half, and people were putting huge trolleys of food through the clothing tills. There are tills in the food section with conveyor belts, and the ones in the clothing section are just a counter (that's normal I think, isn't it?). And not just biscuits and chocolates, but raw meat, fish, veg.
I spoke to the cashier, and all she said was 'It's very busy in the food section. We can wipe it if you want'.
So, AIBU to not want to put clothing I'm buying on a counter where someone else has put smoked fish, or wet frozen food?