Bargaining with project developers is a contractual agreement and so, a bounty manager among other things can and indeed should introduce escrow as condition for accepting to handle the bounty. And I believe this will help to flush out fake, ingenue and scamming bounty managers out, this place will be cleaned up.
This escrow is very possible as I have seen a bounty manager successfully doing that with at least two bounties that I know of, with escrow boldly stated. With this kind of escrowed bounties, you don't have a choice than to be committed and give in all because you are sure at the end, you will be rewarded accordingly, no waiting for exchange listing, launching of website crap stories, refilling of another form which will deny hunters who didn't see the information because they have moved on , or KYC.
So far, Julerz12 account as a manager has successfully done escrowed bounties. I guess two that I know of, below is their bounty thread links we can check :
https://bitcointalksearch.org/topic/endedno-kyc-geoma-dao-cares-for-the-future-bounty-pool-wescrow-5223521
https://bitcointalksearch.org/topic/ended-ieo-bmyguide-connecting-travellers-all-around-the-world-wescrow-5208770
Other BM should adopt the escrowing bounty rewards style