Is it permissible to accept gifts offered due to one's professional position, whether presented before or after the provision of the service?

It is not permissible to accept gifts offered by clients due to one's job, because they are a cause for inclining the heart and showing favoritism in work. Umar ibn Abd al-Aziz considered them a bribe. The proof for this is that the Prophet, peace and blessings be upon him, disapproved of the gift given to Ibn al-Lutbiyyah, which was presented to him because of his work.