Exchange requires clear ownership rights, and with those rights go equally clear obligations. All exchanges place upon the seller the obligation not to defraud the buyer. A food seller must not poison the buyer, and claims of the qualities of the food do not constitute a defense. All countries have legal systems that enforce the obligation of the seller to adhere to basic standards without which exchange would be impossible or severely limited. Governments enforce property rights and the obligations associated with them. The regulating government cannot in most cases be local if commerce extends across national or international markets. This is why the US constitution grants the federal government control over commerce (Article 1, Section 8, Clause 3, the “commerce clause”).