This is the big question. The political and social climate of the vote buying days is clearly gone, but this does not mean it can't arise again, and we must be on the watch. Oregon is not so special -- any state that allows mail-in or offsite voting is vulnerable.

Actual vote buying, for cash, seems a harder crime to get away with in the modern world, especially if we did set up a program where any vote seller could turn in a vote buyer and get amnesty for that particular vote-sale. (Those who did not turn in a vote buyer in time would not get amnesty.) We also have facilities for anonymous whistleblowing as an alternative. If the vote buyer is a mobster who will break your legs for turning you in, however, amnesty doesn't help.

Of course, it must be cheaper to buy a vote outright than it is to get one through legal means, such as advertising and get-out-the-vote techniques. With 50% turnouts, get-out-the-vote (such as driving known supporters to the polls, calling them on voting day) seems much cheaper at vastly lower risk.

Of course the goal of vote-at-home, like Oregon, is higher turnout. In this case I presume workers, rather than driving voters to the polls, just stop by and ask in person if they voted, which might be very persuasive.

As noted, I have more concern over pressuring voters, with force or peer pressure, than doing it with actual cash. That's much harder to stop or make illegal. If a group/church/union/party has any excuse to ask for your ballot receipt, this could generate a large increase in such pressure.

However, in this debate there will be a lot of discussion about which threats are truly the most dangerous. If we look at vote buying, which is close to non-existent today, how do we scale the risk of its return over quantities which are much larger today, such as the number of people who don't vote at all for various reasons, or box stuffing, or voting machine manipulation. Should we fail to address a real threat doing real damage because of fear of something that might become worse someday? It's a hard question.