I would have suggested a formalin dip prior to tank transfer.
The problem is that many LFSs run sub-therapeutic levels of copper to mask disease while they are in the store. Once they get into QT, viola, the disease emerges (e.g., brook). I always bring a vial and ask for the LFS water when I buy a fish locally (which is becoming less and less). And essentially all the stores around me are running low copper in their fish systems. Thus, with clowns, I assume they all have brook and do the formalin dip prior to TTM. Buying from a LFS that has the clowns in with coral can be safer (obviously not running 0.1-.2 ppm Cu with coral), but still obviously need to QT.
(I get a vial of water so I can test it prior to opening the bagged fish -- I have also seen people use syringes to get water from the bag and reseal while testing, but the vial is easier).
Most of my purchases these days are from Diver's Den. I still do a full QT (I got an assessor that developed ich in QT), but it's going to be very rare to see a fish come from DD with brook, etc.