A thought:
- The Detached Duty Office makes surplus IISS starships available to scouts that will help the IISS in its missions. The surplus IISS scout ships are not given to the scouts, the scouts are allowed to use IISS vessels.
- The Intelligence Branch of the Detached Duty Office debriefs detached scouts when they visit scout bases for refueling or maintenance.
Therefore, there would a powerful motivation for the IISS to make free maintenance available to scouts with surplus IISS vessels, because they would be maintaining their own ships. IMO the IISS would strongly prefer scouts bring surplus IISS vessels to Scout Bases for maintenance, instead of Crazy Eneri's Discount Parts and Maintenance and Groatburgers. IISS engineers know The First Rule of Scout Ship Maintenance: There are not supposed to be parts left over. Another reason is that giving unvetted maintenance personnel access to scout ship systems would be a serious espionage vulnerability. And that's another reason the IISS would want the ships maintained at their facilities, to check for trackers and other espionage devices.
Free fuel with be a strong draw for scouts to come in and meet with an Intelligence Branch debriefer, and the scouts who even have surplus vessels are supposed to be helping with the IISS' mission anyway.
The IISS isn't making these services available to scouts with a surplus vessel as a benefit, they're servicing and refuelling their own vessels that are on mission. They're indirectly on mission, but still on mission.