I don't think we're in as much disagreement as you may think.
By "voided", I mean a voter voluntarily says that they messed up and wish to get a new ballot. This is done routinely because of mismarked ballots, etc. The scenario here is simply that a voter accepts an offer to sell their vote, marks the ballot in the proscribed way, takes a picture, voids it, and then submits a new ballot with their actual vote.
In New York (and in Washington, where I used to live, before they went mail-in only) after marking your ballot (in NY with a pen, in WA on a screen and getting a printout) you put your ballot into a machine which scans the ballot and puts it in the local tally, and dumps it into a cardboard box, as you say, you counting later. That's the "machine" I'm talking about.
By the poll worker's presence, I simply mean that if the vote buyer requires a video of the ballot being filled out and put into the machine (or the cardboard box) the poll worker will notice that the person is taking a video and will ask them to stop.
Rather than preventing people from photographing their ballot through enforcement, this just makes the value obtained for "buying" a vote lower, thus serving as a disincentive. I mean, a vote purchaser could just take people's word for it too if the purchaser is not worried about being tricked by "unscrupulous" voters.