All looked good until they wanted complete credit card info including security code or they would open a line of credit with the "pay later" option which will ding your credit score when the total for the order was zero and zero shipping looks like a harvesting expedition.
But if they DING you CC you still have a receipt to contest it. For all you know they might never ship at ZERO cost. They will probably be sending you a email informing you of the price mistake. BUT ...BUT if they don't, then this becomes an awesome deal.
If they cancel, they might send you a few coupons to compensate for the trouble.