Question

How important was the accuracy of Ida Tarbell’s research about John D. Rockefeller?

It was not that important, as long as she received a large readership for McClure’s.
It was non-essential because it was not a legal report.
It was essential for her credibility as a journalist.
It only mattered a little because she was not a lawyer.

Answer 1

The accuracy of Ida Tarbell’s research about John D. Rockefeller is very important because 
It was essential for her credibility as a journalist.

Ida Tarbell's mode of researching about John D. Rockefeller and the Standard Oil company includes:
1) interviewing dozens of Standard Oil employees.
2) visiting Standard Oil headquarters in meetings with a representative of Standard Oil, Henry Rogers
3) visiting Rockefeller’s Baptist church where he continued to serve.
4) scrutinizing 300 testimonies, each approaching 1,000 pages of text as part of her research.

Her thorough research lent her the credibility to write her series about John Rockefeller, the start of the oil industry, and how it became a monopoly.