on the up and up

Before I Say Good-Byeを読んでいます。政治家のMacは孫娘のNellがAdamと結婚する際にAdamとは別に税の申告をするように注意をしていました。そして最近、ボートの事故で死んだと思われているAdamが不正な建築に関与してた疑いがでてきました。
She remembered that when married Adam, Mac had warned her to file income tax returns separately. “Nell,” he had said at the time, “you intend to have a career in government service. That means the vultures will be circling around you every inch of the way, looking for some misstep on your part.
...
“Yes, Mac, I filed separately,” she said tightly. “So stop worrying.” She started once more to step outside, then turned back again. “But level with me. Is there anything you know--hear me out--and I mean know that would suggest Adam wasn’t on the up and up?”
“No,” he said somewhat reluctantly, shaking his head. “Nothing.”
慣用句に違いない "on the up and up" の意味を調べます。
・Collins Dictionary: If someone is on the up and up, they are honest and sincere. [US , informal]: I'm a pretty good judge of men. If you're honest and on the up and up, I'll be able to tell it.
・Cambridge English Dictionary: Someone who is on the up (and up) is honest and can be trusted.
・Merriam-Webster's Online Dictionary: an honest or respectable course--used in the phrase on the up-and-up
政治家をこころざす人は配偶者の行動・言動等にも注意しなければならないことは最近の日本のニュースを聞いていても良く分かります。