I used to believe all pool guys were quacks but they have a different priority when maintaining a pool, outside of money and billable services. They are looking for an answer that has to last 7 days without care. When you are doing the BBB method you learn in PoolSchool, you learn you need to measure the levels daily and make decisions and take action for that day. Tomorrow, you will make another decision based on testing and take the needed actions.
The Pool tech cannot do this, he (or she) must test and make a decision that needs to last seven days. When he returns in 7 days, he will determine the consequences of his actions and make another decision. He cannot return tomorrow night to test again.
The pool$tore is somewhere in the middle but with less practical knowledge in most cases. They may be focused on getting YOU to make a decision to BUY what they recommend to last until the next time you come into the store.... or to make recommendations that encourage you to return in a few days with more water and another opportunity for your to make another buying action.