I have heard this from several friends, and a neighbor. They voted Republican down ticket all the way, but couldn’t bring themselves to vote for Trump. I suspect there are many people that feel that way, and it’s obvious in New Hampshire, with no allegations of voter fraud.
At the most, I’ve heard stories that you get some college students in Dartmouth and elsewhere that reside in NY or MA, but will vote in NH. Really the only sort of “fraud” that you might think about. See my above post for even more of my guesses.