The first source is a press release from what appears to be an HR company which attempts to debunk the claim that agreeableness correlates with lower income based on a survey they contracted through a polling agency.
That survey portends to show that "almost half of American workers (45 percent) believe employees with more agreeable personalities (those who seem more tolerant, less controlling, or more willing to consider co-workers’ ideas) are more successful in the workplace". There are a lot of problems with this statement...
(1) Less than half of American workers actually agreed with the stated result.
(2) The study survey was carried out by a local North Carolina polling agency with no data available as far as I can tell.
(3) Believing that 'agreeable' persons are more successful in the workplace does not contradict the finding that 'agreeableness' correlates with low incomes -- as in many cases, what many individuals believe does not necessarily correspond to the truth.
The study they apparently contracted the survey in response to was called, "Do Nice Guys – and Gals – Really Finish Last? The Joint Effects of Sex and Agreeableness on
Income" [1]. Needless to say, you'll want to skip the press release and go straight to that paper.
I am unable to read the second source, thanks to Elsevier's brutal lockdown of scientific research. That being said, I'm hesitant about buying into the thread parent's claim that TFA "contradicts the current state-of-the-art in psychology research" given that I have only been able to find that one study purporting to link "agreeability" with lowered income.
[1] http://www3.nd.edu/~cba/Nice--JPSPInPress.pdf