I almost did this last night in MCO. Needed one volunteer, and I had bid $800 in the app, so I approached the podium. GA took down my info and I waited to board, about halfway through boarding, she protected me on a later flight but said we would have to wait until the end.
Once everyone boarded, she said she needed my seat, and would print the voucher shortly. I said "for $800 right" and she laughed and said, "no, $500, we don't use bid numbers." I replied, "Okay, I'll stick with this flight then."
She called a supervisor over who told her to go to
#2 on the list (although was fairly certain I was the only one who had been waiting to board), so she paged another PAX. I hadn't boarded yet so I thought about it, and then took the $500. When the other PAX got to the podium, the GA said, "sorry, there's no room for standby on this flight" -
It was 100% a bluff, and she got me!
I was happy with the $500 ultimately, and I cant be mad at the bluff, because I was doing the same. Won't get me a second time though!