I live in New Hampshire. State representatives in the GOP last year said this is a real issue. Governor-elect Sununu said that the state is "busing people" from Massachusetts to vote for Democrats (I don't think he was specifically referring to Hillary).
I don't know of any busing, but voter registration lists are public documents. I've seen the one for my town and I saw a half-dozen names on that list of people I know live in Massachusetts which I can prove because I actually have copies of their drivers' licenses for business purposes.
After I voted in the primary (for Bernie) I got a nasty letter from the Secretary of State office saying that if I had an out-of-state ID, I would be stricken from the rolls. This is very insulting first of all because not only did I show my in-state license when I voted, to prove I wasn't committing fraud, but many people who can't show an in-state license are allowed to vote.
Why? Many people have already said that elections offices looked for first time voters and targeted us because we were more likely to have voted for Bernie.
Now would be a good time to end this shit of "when their party does it, it's bad". The hypocrisy is nauseating..
EDIT: And these are NOT people who used to live in NH who moved to MA. They never had a primary residence here.