Say you bring a new widget to market, as a small business, and you start selling via FBA. Pick your favorite kickstarter project and imagine it's you.
There are thousands of sales tax jurisdictions in the US, between states, counties, and cities. There is no way you, as a little guy, can manage all that.
It's not though. If I live in California and have a presence only in California and ship a widget to Pennsylvania, I'm under no requirement, as a matter of constitutional law, to collect PA state sales tax on that purchase. What the buyer states, on their own state tax forms, is their own business.
This specific case, about sellers affiliated with Amazon but not part of Amazon, is ultimately for Amazon, its affiliates, and the states to resolve. There isn't a role for an independent startup. The same would apply to present or future networks of sellers in the same vein.
Your response is why my other related comments mention only through legislation this gets fixed. Everyone is complacent because no single entity is held responsible, and people are evading taxes because of it.
Attempting to justify tax evasion with constitutional law is unacceptable.
Or states simply figure out more reasonably enforceable and appropriate revenue sources. A number of states already get by without state sales tax of any sort(1) so that's not an unreasonable option. To the degree that collecting sales tax on interstate purchases is difficult yet, perhaps, increasingly important, I'd suggest that eliminating that dependency is a better option than increased government intrusion.
Personally, I'll be sure to vote against any representative who advocates for databases of online purchases or anything in that vein.
(1) Sort of. NH, for example, does have a relatively high tax on meals eaten in restaurants.
There are thousands of sales tax jurisdictions in the US, between states, counties, and cities. There is no way you, as a little guy, can manage all that.