This site might not exist if it wasn't for pool "professionals" that don't actually know how to care for a pool. Mine was mistreated, and eventually destroyed, by the "best" pool maintenance company in my town (fancy logo, lots of trucks, etc). Now that I know what I know about pool care, I'm stunned about how little these guys knew. TFP works. It's proven science. And there are thousands of posts here that demonstrate that pool store advice very often does not work long time. Stay the course with what you learn here and you'll have a successful pool. Stay out of pool stores (except to buy chlorine and acid and CYA).
I let my local pool store test my water every so often because I like the little squirt containers they give away for that purpose and for the 5% discounts they email me for letting them test it. Other than that, I ignore their advice and their test results!