Buying online and picking up in-store is a free and convenient method of shopping. However, I would highly recommend inspecting the items before allowing the cashier to finalize the purchase.
Here's why? I made an online order to pick up in store at Home Depot. The cashier grabbed my item and receipt. I stopped to inspect my purchase and it was damaged and the item was out of stock so I could not get a replacement. I returned the item immediately but the money has not been refunded yet to my card. It has been over a week but per their policy refunds could take up to 6 to 10 business days.
My lesson since is to kindly tell the cashier you are here to pick up your online purchase order (provide barcode, drivers license, the protocol of that store) but may you see the items first before finalizing the order. That way if the item is not up to par or not what you expected, you can cancel instead of being charged and returning then waiting for the funds to be returned back to you.
Source: Personal Experience