why did the team of the Der Stern magazine so easily accept the authenticity of the first sample diary?

The team of the Der Stern magazine so easily accepted the authencity of the first sample diary because they were so eager to publish the most controversial document and achieve sensational reviews.

Explanation:

On 25th April 1983, the Stern magazine publicized that it would publish the diaries of Hitler found by one of their star reporter. The announcement created sensation in the media industry.

Since Hitler's death, the documents which would show posterity the truth of my [Hitler's] actions were on search. Many people searched for the documents, supposed to his diaries.

So, when the Stern magazine found a lead of finding the diaries, they accepted the diary without checking its authencity. As it would achieve sensational reviews and money in return, to the company.

pretty sure a is right