There is no saying who will be and will not be fair. For the sake of impartiality, there should be no obvious bias towards any certain candidate. If they do have a preference, they should make it difficult for the viewing audience to notice what it is and focus purely on the debates.
Most presidential debate moderators are not fair to Republican candidates. It is unlikely that these moderators will be fair to Donald Trump. Yes, Trump has created a lot of controversy with his bombastic statements. However, Trump deserves a fair debate, just like Hillary Clinton does. Therefore, the debate moderators should work hard to ensure a fair debate for both candidates.
I do not believe the moderators will be fair in the presidential debates. There is too much at stake for the moderators to be neutral. They will most likely give their favored candidate more time to speak, and more leeway with their answers. This election season has been extremely polarizing, and tensions are high for who will be the next leader of the United States.
While the debate moderators might be 'fair' to Hillary Clinton and Donald Trump, they are certainly not going to ask the hard-hitting questions that the American people deserve. I'm imagining that it will be an hour or two of listening to pre-planned talking points and veiled insults about the other candidate.