Moshe Rosman is the historian of the founder of Hasidism who dug into the tax rolls of the 18th century Międzyboż to find that
Międzyboż tax registers list a certain “Balszem” as residing tax-exempt in a kahal-owned house from the 1740s through 1760, the year of the Besht’s death. While tax registers may not be the sexiest of sources, they are reliable. Rosman held a smoking gun: the Besht was a real, historical figure, firmly ensconced in the local elite, enjoying a tax-free and rent-free existence.
A new edition of Rosman’s Founder of Hasidism, was just published by the Littman Library and there is an informative review (from which I quoted above) by Glenn Dynner on the Jewish Ideas Daily website. The new edition is titled, A Quest for the Historical Ba’al Shem Tov.