Where did you get the idea that he's the least bought? It's factually inaccurate.

He literally publicly offered oil executives whatever they wanted for a billion dollars, and though he didn't make that much (that we can prove) has been delivering on that promise since. [0]

While being "honest" in the sense of "staying bought" and delivering the promised graft is somewhat commendable, it's not exactly evidence that he holds some sort of moral high ground.

[0] https://thehill.com/policy/energy-environment/4961820-oil-bi...