Earlier quoted context omitted.
$100k of South Dakota revenue is either an almost exclusively local single-owner business or a much larger internet shop. But regardless, that kind of number is a full time job. If you're selling over the internet and making a full time job out of it, you can handle computing sales tax for SD residents. Yes, it's burdensome. Yes, it would be good to have a simpler federal framework for this. No, it's not the end of t…
I think you've got it kind of backwards. The absence of tax collection is what allowed Amazon to become Amazon and this change is now a barrier to a new entity challenging Amazon. Amazon voluntarily started collecting taxes nationwide without a blip to its bottom line. The new law will in fact put Amazon's first-party goods in parity with 3rd party sales. Third party sellers could often undercut Amazon's own pricing…
I personally worked on this sort of problem for a large company; most of the work is in figuring out what the business logic ought to be; turning it into code is (largely) trivial.
Figuring out the logic only needs to be done once, and the payments provider is the natural place for it to live.