This is really interesting to me. Now, I'm not advocating Sanders, so don't take this that way but:
People say they like Trump because he can't be bought. Everybody else is bought and paid for though, except Sanders. It's fine and noble for the President to be above bribery, but Sanders is the only one pushing to change the whole system.
Trump supporters lash out at Hillary for being a liar. No argument there, although Trump lies all the time too. I don't think he has any concept of what is factually true, his truth is whatever he wants it to be at that moment. Sanders hasn't really lied about anything. He does very well when Politifact checks his statements and assertions. Probably better than anybody else in the race.
There's any number of reasons why Sanders isn't a good choice, but it just strikes me that some of the big talking points people try to use regarding Trump are actually more applicable to Sanders.