Depends on the store...I work for PetS****, and we don't quarantine or medicate fish (other than with aquarium salt in the whole system) unless they visibly show signs of sickness...the volume we sell is much more than we have quarantine room for. They come in from a distributor somewhere, we temp acclimate the shipping bags for a bit (although we drip the more ph sensitive fish like neons) and then dump them in the show/sales tanks. Even if the water was medicated...no medication prevents against all diseases and constant exposure to medication creates more resistant bacteria/viruses, making treatment when there is a real issue much more difficult. As well, if the sales person can't tell you how long the fish has been around, you have just as much a chance getting a healthy fish that's been in the tank for months waiting for a home or one fresh off the truck potentially carrying something from the distributor, or the fish that's been around can catch something from the new fish... Again, depends on the store, but speaking as a chain employee (not a representative of the store), there are too many variables and I always quarantine my fish. They seem healthy enough, and I talk to a lot of repeat customers that never do quarantine and claim to have no issues...but there's others that come back looking for a cure for ich or what have ya a week after buying their fish. I don't like to push my luck.