Honestly, an "are you sure" button on bidding is a bad idea.
Imagine a bidding war?
"Bin on this player" - "are you sure?" - "yes" - "sorry, but you have to raise the bet" [another team just placed a bet] - reload page - enter new amount with some "safety gap" - "are you sure?" - "yes" - "sorry, but you have to raise the bet"...
The only way I could imagine this to happen is adding a "disable reminder" option in the preferences, which would lead to transfer active coaches like you and me disabling it within seconds.
Zwei Dinge sind unendlich, die Dummheit und das All...