Depends on the state in the US. Almost every state has relatively strict requirements regarding which models of scales may be used for trade (pricing), and some impose taxes and other fees to keep them in operation. Most scales on grocer floors that are accessible to customers (if you can even find them these days) are clearly marked as "not legal for trade" or have a similar disclaimer -- precisely because it would be too expensive to keep carefully calibrated trade-legal scales exposed to the general public.