To be fair to them, they bunny might not have been available for sale at that point if anyone had asked, they might have just not moved it out the back. I'd have thought that taking sick animals from the shop floor would be good practice but not necessarily a legal requirement as long as they don't sell it. The fact that she said it's on Baytril suggests they know it is poorly and are treating it. Whether Baytril is the appropriate treatment is a different question. As it's a prescription only drug, in theory bunny should have seen a vet in order to be given it, although it wouldn't surprise me if some places manage to keep a little stockpile somehow.
In all honesty, although it doesn't sound perfect, it doesn't sound an urgent problem either. If you're still concerned, why not ask to speak to the manager to check bun has seen a vet and to suggest bun is taken out of public areas to get well without constant shop floor disturbances.