Ask HN: US sales tax for ecommerce “platforms” (not sellers)

Suppose I am an ecommerce platform - I don’t sell any of my own products, but am merely a conduit for other entities to sell their product to consumers. Am I still responsible for sales tax on B2C sales?

What I’m really selling in this case is the use of my platform/service to the actual B2C sellers on my platform. So my sales tax ought to be based on what said sellers pay me, and what jurisdictions they’re based in.

Is this understanding correct?