I don’t see any problem with negative bids.
Let’s say 2 players are bidding for Allies for the reason that it is the league rule, and in reality, each would be willing to bid below 0 (in other words, they both think the Axis need a bid, and are unwilling to play the Axis without extra units)
Say Player 1 is willing to take Axis +6 and Player 2, Axis +3
So they start bidding for Allies, and the bid keeps dropping, because neither is willing to give the other player the Allies with a bonus. It drops to 0, but the other player (who did not bid 0) is not willing to take the Axis at +0. So the bid goes negative, meaning they are willing to take the Allies even if it means the Axis get starting units.
If Player 1 bids -3 or less, then Player 2 would stop and award the Allies to Player 1, and then apply the bid which is now an Axis bid.
For example, Player 1 bids -3. Player 2 is not willing to take the Allies when giving up more than 3 to the Axis, so he says “you win”. A -3 bid for Allies means that the AXIS player would choose the bid (an infantry somewhere or 3 IPC’s to any combination of treasuries).
Eqqman, you are mistaken when you say that bidding a bigger negative puts you in a better position.
If Player 2 were to bid -6, that means he is willing to take the Allies, giving up SIX IPC’s of units, which is a raise of Player 1’s offer to give up THREE IPC’s of units.
There is no problem with negative bids, and no need for a rule to outlaw them. If you outlaw them, and both players want to take the Allies even if it means giving IPC’s to the Axis at start, then whoever bids first could bid zero, and the other one is SOL.