I sat as a Republican to assist in submitting absentee ballots at my county clerk's office. The person I was working with seemed really irritated that I wanted to view the ballots instead of just allowing her to read to me and have me mark the paper. I can't say any votes were stolen in this manner (intentionally reading off the wrong information) but the possibility was there, if I did not insist on seeing the absentee ballot myself.
I should be clear: This happened to me during the 2018 mid-terms, not the current Presidential election.