Am I right if I think supermarkets are making only a 3 percent profit?
Were I in such a business, I would expect at least 10 percent or more.
So they are undercharging us?
Time to get realistic?

"Am I right if I think supermarkets are making only a 3 percent profit?"

A bit of slight of hand there, at the check-out supermarkets make 3% net, but as they control the supply chain they make profits at all points along that chain, from farm production, packaging, wholesale, transport etc.