Back in the 70’s I was en election judge for about 7 years. We voted at the rec room of of a Texas Prison Farm, very rural. We never had any issues like that but it was a democratic area back then and I never was sure what was going on at the county court house when we turned our votes in. Part of the time we had those big walk in voting machines .
If the people counting the votes aren’t honest anything can happen.
Through my career I have a pretty good eyes for spotting how something can be gamed. It is real easy to game a polling place. First, they use volunteers, some that are not up to the task but they volunteered to why not allow them to work the poll. This leads to even the procedures in place not being followed. Add to that people that are real clever at the polling stations are no match.
For starters, poll workers should be county employees properly trained, not volunteers paid for the day. That would be the first big necessary step.