Isolated with meds generally means they run a prophy dose of copper. This can mask a ton of stuff. My LFS does this.
However, it could also mean that they quarantine each new fish in a disinfected system 12-15' away from other systems for 2 months treating them for everything from ich to internal parasites.
Does their warranty also cover you needing to break down your tank and disinfect it if you get Amyloodinium?
I would spend a large chunk of time reading the sick fish forum and the stickies there...I don't mean to be a jerk, but your being naive about infection and re-infection. A sick fish can be "eating and healthy".
I recently had two "eating and healthy" fish die new years day 5 weeks into QT within hours of each other. Very happy that they were not in the DT.
Good luck!, and the cost of a QT setup is marginal. Look into it prior to your next purchases.