Economic nexus policies for marketplace facilitators have settled in recent years, but retroactive liability for prior periods has emerged as a significant sales tax liability risk for online marketplace facilitators. A pair of 2026 state court decisions from South Carolina and Wisconsin illustrates this significant and converging trend in state sales tax jurisprudence for online marketplaces. Amazon Services, LLC v. South Carolina Department of Revenue and Stubhub, Inc. v. Wisconsin Department of Revenue are indicative of the sales tax exposure risks for online marketplace platforms under pre-marketplace statutory frameworks.
In high-stakes legal practice, the author of this article frequently encountered state tax authorities enforcing similar, and arguably retroactive, policies for pre-marketplace law tax periods, despite assurances in law and guidance that marketplace obligations would not be retroactively enforced.

