In an effort to circumvent existing sales tax nexus standards as set forth by the US Supreme Court in the Quill case of 1992, states have enacted a complicated web of legislation and administrative policies that include economic nexus and various use tax notification requirements
South Dakota's economic nexus standard was challenged by Wayfair and reviewed by the US Supreme Court in April, 2018. On June 21, 2018, the US Supreme Court ruled in favor of South Dakota; abrogating the Quill physical presence standard. You can expect to see additional economic nexus legislation at the state level as a result.
Download this guide which highlights the issues.