There are several bounties that rewarded with tokens that already in the exchange, so the bounty hunter could calculate how much they work will be paid but also it's not the exact amount because the price of the token could be up and down. I think if bounty hunters joining a new project bounties they must have analyze the project itself before joining because there are many projects ended scam or the reward are not entering exchange after the presale.
If that's clear, because I also always analyze every bounty that I participate in so that I can make my own conclusions before following it carefully, especially if the token is already on the exchange, this will really help the bounty participants in making a certain amount based on the allocation that has been made provided on the bounty page itself.