In my experience, when someone refused was because he/she forgot to bring the reward.
Some time ago, before Slack, we used to type "donuts" in the email's composer and send the message to the team's mailing list or to the full office.
Imagine your co-worker on the next day with two or three dozens of Krispy Kreme products.
I have an unrelated question: Have you ever thought in a new release of your book on Riemann Hypothesis? The price is not a problem but the UX.
I got a hard copy that sadly is falling apart after some usage. Being truly honest, after seeing this I searched for a pirated PDF copy to finish the book.
Original author seems to be based in France, so I don't think FCC limits are being into consideration. Would be interesting if there exists an equivalent limitation by EU regulations.
At international level, encryption in ham bands is forbidden (at least).
Imagine your co-worker on the next day with two or three dozens of Krispy Kreme products.