I know , however I've received a negative feedback from BedBear so now I'm not anymore an escrow and I hope he and the other moderator (Eal F. Skillz) will remove the negative feedback.
Negative trust feedback was put to notify others that you have failed to do the job, however, I think just an untrusted feedback or a post on your escrow service thread was enough for this, so people looking will see it. I hope you won't stop the service because of this.

~~MZ~~
There is no way to choose trusted/untrusted feedback, if the person who left the feedback is in your trustlist the feedback will show up as trusted. I personally think maybe a neutral trust is more appropriate in this situation, but if BadBear thinks he deserves a negative thats his choice and if people don't like it they have the option of removing BadBear from their lists.
I would say a negative trust is much more appropiate. His lack of a willingness to accept personal responsibility in this situation shows that he is not willing to cover any mistakes that he makes. He implied that he was not going to reimburse the lender for his loan (Moreia would almost certainly not repay his loan if his collateral is gone).
This is very similar to him accidentally sending a payment address that he does not control the private keys too and then not covering the loss.