Of course they should not have asked for a refund if they scrubbed a non stick item.  Buyers need to take responsibility for their own actions and not blame sellers for everything.

They would not have been refunded in a B&M store if they used something incorrectly.  What would they have done...picket the store to discredit it for their actions?

That is what this buyer has done to you...they have discreditted you because of their actions.