We recently had a student send us a screenshot of their Moodle gradebook claiming to have gotten full marks on all 7 course assignments while our records showed that the student has not even attempted the assignments. Seems like a major Moodle issue!
However, being the suspicious type and based on great faith in Moodle, we did some digging and we now have lots of evidence (gradebook comparisons, activity log reports) that the student had in fact displayed their gradebook from another of our courses then changed the html of that page in an editor before redisplaying the edited gradebook and creating the fabricated gradebook screenshot which they sent to us. Note we were able to reproduce this process ourselves.
So, instructors should be aware of this possibility and trust their faith in Moodle accurately tracking student activities.