I always gamble and scan any alcohol or age restricted items first. About half of the time, it throws an alert and flashes but lets me continue scanning, it just won’t let me complete and pay until someone has come over and approved.

For some reason though, some idiot designer who never actually thought about how these would be used in reality, decided to make it so that the other half of the time it immediately stops all scanning until someone comes to fix it.

In the first case, basically I waste no time. In the second, I lose however long it takes for the cashier to come.