Is it permissible for the second partner in a commercial shop to grant a discount to a customer who had already received a discount from the first partner, without the knowledge of the first partner?

If a partner deducts from the selling price by way of donation or favoritism to the buyer, he is not permitted to do so without his partner's permission, whether the permission is verbal or customary, because customary permission is like explicit permission.

However, if it is not a donation, but the partner sells at a lower price for the benefit of the trade, this is permissible, because a partner is allowed to act in ways that benefit the trade and do everything that is in the interest of the trade by virtue of the partnership.