You are correct that SCOTUS accepted the concept of a de minimis number of transactions or dollar amounts but did not specify what would qualify for de minimis - only that SD's $100,000 or 200 transactions met their standard.
The real abomination here is that the US Congress has not passed a law that would make filing these multiple state returns less of a burden for smaller business' that do not have a physical presence (nexus) in a state. Each state has their own filing requirements, forms and items taxed and the rates taxed, which makes filing a nightmare for small business ' filing in multiple states where they do not have a physical present.
The "marketplace facilitators" like Ebay and Gunbroker are considered the seller and must aggregate all transactions. They're stuck and we're screwed.
