Parties choose their candidates. While it is democratic in the sense that people cast ballots; the process was never guaranteed to be a level playing field. Sanders was an outsider from the democratic party. The party has rules and systems to keep people like Sanders out. That is what super delegates are for. You and I may both have preferred Sanders, but we don't have a right to the DNC's private email.
As for the polls, in Canada we do a simple pencil and paper system that works extremely well. You might be able to get an extra vote or two here or there, but the process is essentially unbreakable.