Is it permissible to work as a courier for a service where the final delivery cost might change at the end? Usually, the price is fixed, but occasionally it increases slightly. Customers rarely know about this change, but the amount is small, and they are willing to overpay. What is the best way to act: ask for the initial amount (though the service will still deduct its commission from the higher final price) or take the amount automatically indicated at the end of the trip?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

The basic principle is that the fee in a delivery contract must be known from the outset, or determinable in a regulated manner — such as a fixed amount per kilometer, for example. Ibn Qudamah said in Al-Mughni: "It is a condition regarding the compensation in a lease/hire contract that it be known. We know of no disagreement on this." (End of quote)

Based on this: if the service or application is the one that automatically determines the final price according to a known system, and this price is the amount actually due from the customer, then there is no harm in taking the amount that appears at the end of the trip, so long as the customer is bound by it according to the application's terms which he agreed to.

Allah Knows best