There's a store called Bulk Barn here in Canada where cashiers still do this. Everything is sold in bulk (flour, nuts, candy, etc.) out of giant tubs with scoops, that customers use to fill clear, unlabelled bags. The cashiers have this spinning cylinder thing that lists all the prices, but I've never seen them use it. Instead, they plop each bag on the scale and type in the code, which takes two seconds each.

I don't know how they tell the difference between all the generic powders that look the same, like white flour and rice flour, but they do. And if they don't, I suppose they just ask the customer.