C172 flight instructor on training flight with student reported a ground conflict during landing rollout.

Narrative

During a training flight; my student and I were practicing landings on Runway XX at ZZZ. Upon one of our landings a fuel truck from the FBO was about to cross the runway. The FBO's procedure of having a fuel truck cross the runway is to have the dispatcher in the FBO call on the ZZZ CTAF 'fuel truck preparing to cross runways'; the dispatcher then radios to the fuel truck they can cross if no one replies. As the FBO was making their radio call for the truck to cross; my student and I were on our landing roll out. The fuel truck had already started crossing Runway XX-XY at taxiway X before the radio call was finished; this blocked us from transmitting on the radio to alert them. At this point the plane had reached the point of the runway between taxiway X and Y. My student had applied heavier braking action and the truck had seen that we were still on our landing roll out; which prompted him to brake to ensure there wasn't a collision. Better situational awareness; and the ability to have the fuel trucks radio on the CTAF themselves would prevent this from happening again.