There's no pest free LFS it's just isn't cost efficient, I haven't seen any store that runs independent systems for their livestock, so if a pest free shipment of captive bred clown fish end up being in different tanks on the sump/filtration system of wild caught hippos, I'm sure there's got to be something, even if you left a healthy looking fish in QT for 2months with out any treatment, there might still be a chance of something breaking out a year after he's been in DT, if DT was neglected or some how the fish got stressed out.