Anything that only works if the STORE installs something will fail. If the store wants to help, fine, but the system must work even if the store is actively resisting. That is, activists must be able to enter the store, match up UPC codes they scan in with names of products, quickly and efficiently, to log the whole store, identify the worst products... and rate the whole store as to moral goodness... using the community's concept of what sources or ratings are trusted in TCE.
It is not worth doing if the retailer must install junk before the whole thing works. Some will, and will attract moral buyers, but some won't, and it's quite important that people be just as able to use the system when they are buying in an unfriendly store as in a friendly one.