Just don't be surprised if you don't get him back. Pet stores often dont bother treating the animals, do whatever with them, then tell you a) it was rehomed b) it passed away c) anything else they can think of to excuse themselves for not treating the animal.

If you could, I would get him back now and bring him to the vet yourself. You can quarantine him in a seperate area of the house, a room and ban the other animals from it, and wash up and change your clothes in between animals.