i know some petstore can ONLY sell healthy pets... so before going back and saying.. hey my pup is sick i want my money back, do some investigating to see if that store had a policy on healthy pets... if they do have a policy on that (you might need to see what the laws are in your province.. if they have any regulating pet stores) make sure you have it written and in hand when you return to the store to get your money back. i have a feeling if you go in there with dog in hand saying he is sick i want my money back they will say they have no such policy. it will also be helpful to have your receipt to prove that you did in fact buy him there...
sidenote.. i've visited PEI... love it there