Is it permissible to work in the field of electronic transaction clearance, where transactions are received and sent to another agent for completion in exchange for a commission, without knowing how the other agent completes the transactions, or whether he uses favoritism or bribery?

There is no harm in working as a follow-up agent and processing transactions. This falls under the category of a shared ijara (leasing/hiring contract), and it is permissible for the shared employee to hire someone else for less than their own wage, as long as it was not stipulated that they must perform the work themselves. Doubts about the methods of completing tasks do not affect the validity of the earned transactions, and the general principle is presumed permissibility.