Is it permissible for a marine engineer who works as a ship inspector to shorten and combine prayers due to time constraints and the long distances he travels? Is it permissible for him to accept food and drink offered by the ship's crew during and after the inspection? And does his work, for which insurance companies use his certificates in accident cases, involve any suspicion?

It is permissible for a traveler to shorten and combine prayers. It is also permissible to accept hospitality offered by ship owners, as long as it does not lead to showing them favoritism or overlooking their shortcomings. If it does lead to such, then it is forbidden, and it is better to do without it.

Your job is permissible as long as you do not directly engage in or assist with any forbidden acts within it.