Overall:
Require receipt?
Does payment method matter?

Produce:
No refunds/returns.
No exchanges?

Dry Goods:
Split into departments? (Bulk, housewares, cleaning?)
No refunds/returns on foods.
No refunds/returns on non-food items?
Or offer exchange of equal or lesser value for same or similar item?

Splitting into departments would ensure that houseware items are not exchanged for foods, and vice-versa.

Possibly need to address specific issues, both to educate the shopper on products, end to ensure that feedback goes back up the chain to ordering in the best manner:
Rancidity
Bugs
Unique products: Non-homogenized milk, pickles, flax crackers, etc.

This could tie into the ordering database, with a web-form: Select the department, report the problem, note goes to appropriate orderer or is noted in DB.