[disambiguation]

Outside of math, science, and law, proof and evidence are tricky words. Instead I merely offer a quote for your consideration, from Brad Stone's book The Everything Store (2013):

""" Bezos chose to start his company in Seattle because of the city’s reputation as a technology hub and because the state of Washington had a relatively small population (compared to California, New York, and Texas), which meant that Amazon would have to collect state sales tax from only a minor percentage of customers…. [T]he University of Washington produced a steady stream of computer science graduates. Seattle was also close to one of the two big book distributors: Ingram had a warehouse a six-hour drive away, in Roseburg, Oregon """

In other words, Bezos was well aware of the sales tax advantage from the start.