Learn to use the information resources available to you to track trip ownership history, assignment time stamps, schedule histories, etc. You will see plenty of fishy stuff. PDR it all.

Yes, there are a couple of reason someone MIGHT block their schedule history, but I think it's fair to say USUALLY it's because they are pulling something shady, and not just once, but routinely. These individuals need to be held accountable if they are circumventing seniority to get deals or unethically screwing their compadres.