I don't think the reason behind Trump's appeal is him being honest. Trump lies a lot. He frequently just makes stuff up. I think his appeal is that he gives a one sentence solution to every problem the U.S. faces. How do we stop illegal immigration? Build a wall. How do we prevent terrorist attacks? Ban Muslims from entering the U.S. How do we fix the economy? Negotiate better trade deals. Most Americans are not policy wonks, so they like hearing simple answers instead of Hillary Clinton's longer and more detailed answers for these problems.
I also think the reason why people think Hillary Clinton is dishonest and untrustworthy is ironically because we know almost everything about her. She's been in the public eye for 25 years so there is a long record to look through to find flaws. Most of her State Department emails have been made public, so anything bad in those makes her look bad. However, we don't get to see Trump's emails. We didn't get to see either Obama's or Romney's emails in 2012. We don't know what they are/were hiding, but apparently people are willing to give them the benefit of the doubt on their emails while Hillary Clinton gets hammered because she has been transparent about her emails. Trump has only received lots of public scrutiny for the past year and there are still a lot of things we don't know about him. He hasn't released his tax returns, so we don't know what kinds of business deals he's been involved in. He has no voting record, so he can basically take any position on an issue he wants. Trump isn't very transparent or honest at all, but because he's willing to say outrageous stuff in public instead of just doing it behind the anonymity of a Facebook / Twitter account like many Americans do, he is seen as "authentic" and "real".
