Some federal, state, and local laws prohibit the sale of certain types of plants or seeds that are considered "exotic" or "noxious" weeds. The United States Department of Agriculture prohibits the importation and interstate movement of federally defined noxious weeds. USDA also prohibits or restricts importation of other seeds for various reasons. These restrictions often depend on the country of origin. Treatments or permits may be required.

Besides reviewing the list of prohibited noxious weeds and seeds, buyers and sellers of plants or seeds should also review the state-by-state list regulated noxious weeds, and consult with state and local authorities to determine whether the items they are considering buying or selling are legal in their state.

Many state laws limit the time period after packaging or germination testing within which agricultural or vegetable seeds may be sold. If listed on the packaging of the seeds, sellers should include in their item description the dates of packaging and germination testing. Buyers and sellers of packaged seeds should consult with state and local authorities to determine whether the items they are considering buying or selling are lawful for distribution in their states.