An incident happened in which someone collecting tzedakka money abroad for an Israeli yeshiva was mugged. The driver had dropped him off at the guest house where he was staying, and on his way up with his case containing the money he had collected 2 muggers attacked him and ran off with his case.
He called for help and people from around came over to assist him. He pointed at the muggers running away and said throwing his hands up in despair that he has been destroyed, all the money is lost.
A few of these avreichim chased after the muggers, and actually caught them and obtained the case of money which was returned to the grateful meshulach.. One of the avreichim mentioned, explaining how much of a chessed it really was, that because the meshulach had given up hope, really when they retrieved the case of money they could have kept it for themselves. Giving it back to the meshulach was really a tremendous chessed.
Upon the meshulach’s return to Eretz Yisrael, he went to Rav Wosner to ask about that.
Rav Wosner paskened that it was not a chessed, but was rightfully his. His despair had no affect on the status of the money, because he had no authority to give up hope. The money was not his that his despair would change its ownership status. Because the money belonged to the yeshiva, only the owners of the money, the yeshiva administration, can give up hope and make it hefker, but because they had not even known about it, the money belonged to the yeshiva all along and those avreichim would not have been allowed to keep it.
It is not addressed in the psak, but I wonder about the percentage taken by the meshulach. if he takes 40% (or whatever the actual number is), perhaps 40% of the money returned should be considered a chessed. It might depend on whether all the money goes to the yeshiva, and then the yeshiva pays the collector his commission, or if the collector takes his commission off the top.
Source: Rafi G-Life in Israel