What is the ruling of Islamic law regarding a traffic police officer overlooking violators who are in a weak financial state? Is that considered forgiveness and pardon, or a betrayal of trust?

The basic principle is to perform job duties proficiently as long as the work is permissible, because this is a requirement of trustworthiness and fulfilling contracts. However, if work regulations permit exceptions for certain individuals for a specific reason, there is no harm in that. This is not considered an injustice or a breach of trust, because customary permission is equivalent to textual permission.