IMHO ....
They sometimes try to sample their polls to fall in synch with estimated voter fraud. So it can be difficult for people to know the truth.
However, massive voter fraud normally requires a level of extreme support, not just lukewarm support. And I haven’t heard a soul say that Hillary enjoys much extreme support.
Hence the “Trump is the anti-Christ” narrative on the left, to scare people into voting for anyone other than Trump, even if it is Hillary Clinton.