Last year I was in line at one of the local pool stores (one that starts with "L") buying some start up supplies for the season, I listened to the salesperson "help" one customer with their problem. Salesperson suggested a bucket of CYA, some blue clarifier, etc. All without any kind of water sample, chemical testing or pool size info.

I was amazed at this ability of the saleperson to "know" exactly how much and what chemicals to sell this pool owner to fix his problem. It was truely remarkable!

Still in awe of those "abilities" to this day!