From the petsmart site help tab
ERRORS ON SITE
Prices and availability of products and services are subject to change without notice. Errors will be corrected where discovered and PetSmart reserves the right to revoke any stated offer and to correct any errors, inaccuracies or omissions, including after an order has been submitted, whether or not the order has been confirmed and/or your credit/debit card has been charged. If your credit/debit card has already been charged for the purchase and your order is cancelled, PetSmart will issue a credit to your credit/debit card account in the amount of the charge. Individual bank policies will control when this amount is credited to your account. (If you are not fully satisfied with your purchase, you may return it in accordance with PetSmart's Return Policy.)
So i wouldn't take the chance and get a big bill and have to do hassle of return and stuff.....