There are some bounty that accept negative trust accounts to work with bounty, because the negative trust is not only the result of bad post, but it could be caused by mistakes typing sentences whose letters are incomplete and also sometimes resulting from a user cheat to the account we.
So in conclusion, there are some bounty that tolerate negative trust accounts because they may think that accounts that are exposed to negative trusts are actually good accounts, but there is a small mistake that causes the account to be exposed to a negative trust.