Before they had swipe cards, you could tell who was paying with food stamps. Lots of folks were infuriated to see people in line ahead of them buying junk food and luxury, expensive items with food stamps. Meanwhile working people had to clip coupons, buy store brands or sale items, cook from scratch, or do without.
It was also common to see someone paying with food stamps, then walking out to the parking lot and getting into a luxury car. Though it was considered mean and judgmental to point that out.