Update:  The long standing quesiton about whether or not Amazon will be happy collecting taxes on behave of 3rd party sellers is officially over. On January 1st, Amazon started collecting in 4 more states (HI, IL, MI, and WI)  Last October they added 9  (AZ, CA, CO, ME, MD, MA, NV, ND, TX, UT)  Update - Georgia and Alaska have been added as of April 1st.

That brings the total to 41 (including DC) states that Amazon collects and remits taxes for 3rd party sellers.  (plus there are 5 states that don't charge sales tax) The leaves Florida, Kansas, Louisiana, Mississippi, Missouri, and Tennessee.  The bulk of the other Marketplaces like Walmart and eBay have also complied with most of the rules, but not as fast as Amazon.  For Amazon, the logic is easy

• They have a physical nexus in all 50 states already (so they pay taxes on items they sell direct)
•  They already have an enterprise level merchant collection system that's been running for year
• Walmart, EBay and other competing marketplaces are struggling to move as fast

That leaves 6 states a seller may have to collection sales tax in.  This broader question of tax collection for Amazon (and direct ecommerce sales) is still up for grabs since the South Dakota vs Wayfair decision last year (Here's great deep dive on overall tax impact for a brand - https://www.pymnts.com/next-gen-sales-tax/2019/wayfair-marketplace-facilitator-economic-nexus-ecommerce/)   To tackle that, teams should huddle with their tax team to understand what's next.

The following is the current list as of 4/1/2020.  For full details see: (Amazon account required) https://sellercentral.amazon.com/gp/help/G7VYHGJ8ZT2M58CP.