It appears that I may qualify for exemption from collecting and remitting sales tax on sales to Missouri residents (actually, on sales shipped to Missouri addresses.)

Two of the qualifications for the exemption are not clearly defined in the law (I say as a retired tax lawyer.) And after both writing and calling I could not find anybody in the Missouri Department of Revenue who works with sales taxes who would offer any binding clarification of the requirements. But nobody said they thought I didn't qualify, so I'm taking the position that I do and will no longer collect taxes on Missouri sales. Unless and until the state tells me otherwise.