All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
First of all, you should know that it is not permissible for a Muslim to save his money in banks that deal with usury and interest unless there are no Islamic banks and he is obliged to save his money, in which case there is no harm on him to save his money in such a bank. However, he has to put his money in a current account and not in a saving account. In case we suppose that he saved his money in a saving account and got some interest, then he is obliged to give it out with the intention of getting rid of such money and not with the intention of giving it in charity as Allaah is Tayyib (which implies purity) and He accepts only that which is pure.
As regards taking commission on sold goods based on an agreement between you and the owner, this is permissible on the condition that the goods and the items that you sell are not forbidden in principle.
With regard to Zakat, if the money that you receive from this commission reaches the minimum amount liable for Zakat by itself or with the addition of other money that you possess, and a whole lunar year elapses on it, then Zakat has to be paid. However, if you earn money after this money, then you have to count a separate lunar year for it and you do not have to pay Zakat on it when a complete lunar year elapses on the first money that you possessed according to the most preponderant opinion of the scholars. However, it is permissible to pay Zakat on it when a complete year elapses on the first money, and probably, by doing so, you get a greater reward as you are fulfilling the right of the poor.
Nonetheless, you are not obliged to pay Zakat on the goods that you do not possess even if it is in your custody.
Concerning paying Zakat to one person only, this is permissible according to the most preponderant opinion of the scholars provided he is among the people who are eligible for Zakat which are mentioned in Fatwa: 88368.
Allaah knows best.