Most that I talk to will not medicate if they see ick. They will try to feed heavy, water change etc. Most will not notice flukes, and anything else is usually lethal by the time you see symptoms severe enough past a casual glance.
As
@rygh said, there is a lot of misinformation, advice based anecdotal (at best) experiences etc regarding fish disease.
My 2cents.
Even if I buy from a place that does QT/medication, I continue to do my own QT/treatments once the fish gets to me. Why? Because I can then control and qualify each step. I had an ich free tank for a few years. Each fish was put through TTM and was dosed with several medications along the way before being introduced into my tank.