The Stanford Memorial Resolution to Tarshis, written by John Gurley, 
Moses Abramovitz, and Tibor Scitovsky, cite both reasons for the book's 
sales decline.

http://historicalsociety.stanford.edu/pdfmem/TarshisL.pdf
(page 5):
Before all of this had time to erupt fully, Tarshis’s book was adopted 
by at least 100 colleges and universities, including almost all the Ivy 
League schools. However, the mounting campaign against the book, joined 
vigorously a few years later by William F. Buckley, Jr., in his God and 
Man at Yale (1951), and the appearance in 1948 of the first edition of 
Paul Samuelson’s textbook—soon to sweep much of the market for many 
years—greatly reduced the demand for Tarshis’s own book.


On 12/18/2014 3:09 AM, Roger Backhouse wrote:
>
>
> Tarshis was published in 1947, sold well, and was immediately 
> attacked. Though I have not seen sales figures, my understanding is 
> that sales plummeted very quickly. However, was this because of the 
> attacks, or because of the appearance of Samuelson's textbook in 1948?