I had the same issue a couple of weeks ago.
What had happened was that I had bought 2 cards to the register. Gotten 1 activated and decided not to get a second one.
When I walked out of the store, I went with the wrong card. Got home and got 4002 on trying to load.
Went back to the Walgreen. Store clerk was super helpful and even offered to let me scratch all cards they had in stock to figure out which one was mine. Was also told they had a bunch of cards locked in the managers office which I could check the next day. I declined scratching all they had and went back the next day. The manager had found mine (from the marks left by the swipe on the terminal).
Pretty sure they can't do anything more than that (let you scratch all cards, if at all). So you would be liable.