Which of the following is NOT an example of a decision made using a rule$-$of$-$thumb?

The new promotion plan from Marketing does not feel right to our CEO.

We simply apply a $20\%$ markup to our Cosmetics line.

We allow passengers to board our flights in front$-$to$-$back seating order.

We replenish our stock of breads every Friday night.

We prefer our most$-$loyal customers even if they are not our most profitable customers.