Ask HN: Are P2P Marketplaces Responsible for Sales Tax?

Google has so far been unhelpful in answering this definitively so perhaps HN might have some incite -

If someone were to build a peer to peer marketplace (ex Ebay or Etsy model) in the USA today, what are the requirements for the platform in terms of collecting sales tax on goods sold through the marketplace?

Is sales tax responsibility simply passed down to the vendor? Or are there requirements for tax collection expected of the ecommerce marketplace itself?