Far be it from me to defend supermarkets, but there have been numerous investigations into whether or not they rip off suppliers and each time no one is able to prove anything. They just have significant buying power, which means people queue up to supply them. As for Sainsbury's I think it is expensive but at least they stack stuff on shelves, unlike the scuzzy supermarkets where you have to grovel in boxes on the floor. I hear that in some you have to butcher the meat yourself and the veg still has soil on it. I've never been to one, this is just what I hear.