They need to be consistent and require it every time.
Spot checking is commonly used all the time to different extents (including as you walk through security at the airport) 95% of people don’t go through the full screening but some get pulled aside and do.
Globally this is a common security practice...
And it is normal inside most day to day lives - do you call people/kids/spouse out every single time you see something done wrong? No, you give grace sometimes and correct when needed