Our Co-op (v dingy corner of N London) is quite different. It's smallish and certainly far from glam, but it passes the fresh parmesan/pak choi/organic cheddar test. Just started stocking freerange RSPCA-approved meat, also: big way-hay.
However they do have dependability issues and run their stock very low.
I find the staff charming, far more cheerful than the people in the Sainsbury's local round the corner. I'd suggest you get hold of the manager and tell him/her you'd love to support the store, request things you think would sell.
I think a lot does depend on the demographic: though though this is a scuzzy area, there must be loads of pak-choi consumers out there!