[jakejohnson]

Yes, those platforms may handle sales tax calculations automatically for you for their specific platform. That's only the very first step. Merchants will then need to report and remit their sales tax to each state. If those platforms plan to handle the entire process, trust me they have a ton of work ahead of them if they decide to handle it in-house.

[URSpider94]

Note that popular services TaxJar and AvaTax will do automated filing for you as well.

[ISL]

The remittance is the key, and part of the reason that I've only ever partnered with other companies that can handle that sort of thing.