I have never QT'ed
I have never QT'ed
I check fish/system in LFS, only buy from a honest dealer. First how long they had it, do they treat meds. , run copper, is system isolated or water run thru sterilizer, how are other fish on system(not just that tank). Do they eat well, poop look good, normal activity, eyes and so forth.
Now if you do QT, it is additional stress as most time tank/water quality well be less the your show tank. I would QT longer then most pest life cycles, including egg cycle, probably 2 weeks. Why 2 weeks? Well fish could have one cyst, hard/impossible to see, water cold(Slows developement), falls off, goes free swimming, some attach and still hard impossible to see, the longer you QT the better your chance of seeing. But then theres the stress of the QT tank so you should not go much past what is neccesary to see if fish is healthy.