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):
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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.
""" 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.