Here is the salient fact that many people are missing in this particular logical chain. It’s easy to say and do all the right things and to be non-corrupted when you are a political neophyte. Literally everyone who has ever run for office their first time has done it. What’s hard (apparently, at least based on the evidence) is to remain true to your principles after you win your election and actually get to power.
So what we ought to be looking for isn’t really someone who’s never been tested by the allure of power. History tells us that almost all people fail that test. What we ought to instead be looking for is people who have already been tested, to determine which ones have passed the test with the most success.
The best way to tell whether someone will remain true to their principles is not to listen to their campaign speeches during their first run for office. History shows us those are almost entirely lies (or, more charitably, they are well-meant platitudes that wilt under the harsh glare of reality). Rather, the best way to tell is to look at the actual records they compile after running for office and winning.