Influence of Book Reviews on Book Sales

I was overjoyed to learn that John Watson has secured stable employment with the United States Chess Federation. The French Defense advocate in a great writer and commentator regarding chess history and theory, recently espousing the profound work of GM Davorin Kuljasevic which seeks to eradicate the materialism malady which afflicts weaker club players. 

Also his full time position with the USCF should provide much needed health care benefits. I recall long ago John being ill and seeking contributions from other chess players to defray exorbitantly high health care costs. This was around a decade ago and medical care is even more through the roof nowadays!!

Watson got "beyond material" in his Advances since Nimzovitch magnum opus, so his review/assessment of Kuljasevic's new work should help sell many copies for the Croatian writing talent.  I wonder if it is possible to track John's influence on the gross proceeds for the much awaited book?