I used to run into this problem at Best Buy all the time. They would run ads for cheap memory, hard drives, etc, but by the time you got to the store they'd be "out of stock" and their computer would show the same for all area stores.
I looked into it and what I found out is that the stores have to be able to prove that a certain number of them did exist and were sold. If they run a sale on something that is already out of stock at a good portion of stores, they can be accused of bait-and-switch (yeah, we are out of 55s, but look at this nice 125... it's not on sale but I can "cut you a deal").
So provided Petland can prove that a certain number of them were sold at that store, or from a certain distribution center or something like that, then you haven't a cabinet to stand on.
At least that's what I found out from unofficial sources relating to Georgia laws... who knows what they are elsewhere or even if this is correct.