My answer would be this:  for all the wealth Trump has amassed, his actual power is tiny compared to that of the President of the United States.  If he is this crooked as a businessman, how can you imagine he will not be incredibly corrupt when put into the most powerful office on the planet?  It's not uncertain in my view.  If Trump's corruption is small scale it is because despite being a billionaire he is operating at small scale compared to the United States government.  What he is asking you to do is to let him run the bigtime show, when you already know he's spent his time running the sideshow picking customers' pockets. 

"Nearly all men can stand adversity, but if you want to test a man's character, give him power."  ~Abraham Lincoln

Secondly, add to that the fact that Clinton actually knows how to run the country and deal with foreign powers, while Trump does not.  And he refuses to learn, as is shown by the debate. 

Thirdly, I believe Trump operates on this business mindset:  Any publicity is good publicity, because you don't have to win over everybody and you don't even have to win over the majority of people.  You only have to win over enough people to keep your business going.  So if you cast a wide enough net, even a smaller percentage will do.  I believe that's why he's spent his whole life tending to his public image.  It's why he is obsessed with being on the winning side and never admits to losing in the past, present, or future, regardless of evidence.  This apparently works for his businesses on average (remembering that he's gone bankrupt several times), but it's not a good way to approach the operation of a government that is supposed to work for the whole population.  And I think the way it affects his thinking is very dangerous, because if you can never admit to losing, it's hard to admit you have to change course. 

Two key quotes from a NY Times article: 
Mr. Trump, for his part, sought to blame everything but himself. During an appearance on Fox News on Tuesday, he charged that the moderator, Lester Holt of NBC News, had become overly aggressive with him — although he inaccurately said that Mr. Holt had questioned him over a 1973 federal discrimination lawsuit against Mr. Trump’s company. (Mrs. Clinton had raised the lawsuit question.) He also suggested that his performance was related to a faulty mike — even though he was perfectly audible during the telecast — and that he may have been the victim of sabotage.

The team had primed Mr. Trump to look for roughly a dozen key phrases and expressions Mrs. Clinton uses when she is uncertain or uncomfortable, but he did not seem to pay attention during the practice sessions, one aide said, and failed to home in on her vulnerabilities during the debate.

He apparently doesn't want to study and/or isn't good at it, and these are TERRIFYING qualities for a presidential candidate to have, especially one who is not already familiar with how the government works.  There is a podcast episode by a guy named Sam Harris that I think illuminates this point well.  I will quote a significant section of what he said in a separate post due to its size, and I really recommend you read the post fully.  If you'd like, I do encourage you to listen to the whole thing and see if it convinces you of anything you didn't already know about Trump. 

"There's too much evidence that he knows nothing about the world, and that he does not care that he knows nothing about it.  He's just winging it.  He gives the overwhelming impression of being a con man."

https://www.youtube.com/watch?v=Az1JyDJ_iKU
First excerpt approximately 1:25 to 9:55; second, 11:45 to 20:20

Here's Part 2.  I can't seem to get the embedding to simultaneously work in here and also cue up to the right section. 
The juiciest part probably starts at 8 minutes and 5 seconds. 

Probably comes down to 4chan users not being able to vote in this poll.... a couple of thousand times. Maybe!

But you mostly talked about topics very far away from the comparison base you talked about. I mean, ecology is a very important matter, but not relevant in the matter. What you are saying is that Trump does not have the scale and immorality (from my perspective regarding public servant mission) because he did not have the power yet. But that would make him at most as bad, not worst. And it's not even sure that scam and all translate into corruption. Some can steal their company, not there family, Wall Street is not betting on him.

About not knowing the world, and that's again an other subject, I'm not sure if that matters as much as being willing to do something or anything outside what the very companies and countries that created the problems decides. I mean, look at Putin he is certainly not the best economist and nicest person in town, but he understood quite quickly that by breaking the oligarchy owning the petrol and converting petroleum industry into state owned companies, he could easily fuel 2 decades of growth, improve average revenue and rebuild the military. The only reasons that prevented the previous presidents to do so was corruption, ideology, and legal concerns. Unfair competition (self-regulation, tax, unfair competitors) for economy, unending ISIS problem (bad relationship with Russia and obsession against Assad, free pass to Saudi Arabia) are some of the biggest problems. It could be just as simple as having a little bit of common sense and not do more of the same.

I don't really see where I talked about ecology, but now that you mention it Trump has made extremely dangerous proposals on that topic.  You may not like the EPA's regulations but you probably do not remember the huge problems we have had in the past on environmental issues.  Abolishing the EPA would be tantamout to inviting those problems back. 

If you don't think that the scams he's run on thousands of people over multiple projects, AND THE FUCKING BRIBES HE'S GIVEN, indicate a very, very, very strong likelihood to be corrupt in office as President, I really don't know what to say. 

What I don't think you see is that "not doing the same thing" does not therefore constitute "having a little common sense".  You're proposing trading a crook for a madman, a shadowy figure for a moustache-twirling villain. 

Another couple of quotes from Sam Harris, whom I had never heard of a week ago but whom I like more and more by the day: 

Ecology was in your quote in previous post.

What you don't understand just because you got used step by step to it, because the media describe this as nearly normal is that the current politic is already utterly insane. Obama, Clinton, and even to some extent Bush Jr., they kind of have a good temperament, they speak normally, they are sharp, but it's just the apparence of sanity. We are best friend forever with Saudi Arabia that applies sharia, is lynching women, LGBT, finances terrorism, has racist laws, that does not recognize freedom of religion, corrupts worlwide politicians, buy everything everywhere, put money in Clinton's Foundation, and we are to believe it's normal. And that does not change whoever is elected. And we choose as a foe a country that in case of war can destroy the planet, and let's accuse them of a hacking without a proof to divert from Clinton gross negligeance. I tell you, on that Trump is much more sane, for me he's like basically sane.

Taking the oil (if not an hyperbole) is insane, I give you that. But so was Bush to invade Iraq based on lies, without UN approval, without after-war plan, that was insane, that was criminal, illegal, and so costly it changed USA economy for decades or even generations. And so was Obama to just leave it brutally as scheduled, let ISIS arise, and not fight it efficiently. See the consequences, not just terrorism, but migrations, and all the people that live there, destroyed and some of them enslaved. And Obama is still there, sharp in his speeches, clever and kind of likeable, talking about the responsibility of the voter. This is insanity.

I'm pretty sure you are confusing me with someone else.  If the word "ecology" appears in this thread before you mentioned it, please provide the quote because I can't find it. 

Trump's proposal to take the oil wasn't a hyperbolic exaggeration:  he meant it literally* and we know this because he described what the result would have been (in his mind).  "If we had taken the oil, ISIS wouldn't have been able to use it."  That means he literally was thinking of us taking ALL the oil from Iraq in a matter of a few years.  That's mind-boggling stupidity, and either also evil or just more stupidity.  Even if the current political system is full of maniacs and criminals as you suggest, whose policies are damaging this country, they are at least apparently rational enough to avoid policies that completely devastate the country.  I have no such faith in Trump.  If Trump gets in the White House and the economy doesn't go off a cliff, it'll be because everyone around him is thwarting his every move. 

And there is actually pretty strong evidence that Russia is behind the hacks AFAIK.  It's not just smokescreen.  If you have heard evidence discrediting the idea that Russia is behind it please let me know. 

If the house is full of rats, the solution isn't to set it on fire.

*He meant it literally, unless you admit that he didn't really mean it at all, he was just "completing the rhyme".  Perhaps he only meant to say that we should have taken some oil to help defray the costs of the war, but then he just kept on going to say "and then if we had taken it all ISIS wouldn't be able to take any", which is pure madness.  So the problem is that the more charitable interpretation of what Trump says is that he is such a pathological bullshit artist that he literally does it on autopilot and can't stop himself.  I would rather have a liar than a bullshitter as President because at least I know the liar knows what the truth is. 

In fact, quotes as foolish as the one about taking the oil are what make me so persuaded that Harris is right about what he is talking about in his "completing the rhyme" analogy. Other explanations of some of the ideas he's put forth require him to be so stupid and/or ignorant that even I have a hard time believing it.