Always scenting conspiracies and being certain there are droves of people getting away with all sorts and kinds of cheating is a form of paranoia, and these folks just do not see that. It is like a mantra to them: everyone ELSE is trying to get away with something.
What on earth do they think it would profit any one human being to travel from precinct to precinct to vote all day long? And how many do they think can find the time to do this on election day? And who do they think pays them for this?
When I was working as an election judge, I assure you no one came twice through those polls and every single voter was checked and rechecked. Shoot, we already knew most of them!
Back in the day, when I was a Republican, men from headquarters used to go down to Lincoln Park, our "colored neighborhood" back in segregation days, and stand on the corners and hand out two or three bucks, whatever it took back then to buy a pint of liquor, to all the blacks they could drive to the polls and get to vote. Blacks voted for Mr. Lincoln's party back then. I always thought of it as an incentive to get them to vote, and not as cheating. Never in all my days in politics did I ever run into or even sense any real cheating.