Unfortunately, you virtually don't have a choice. The buyer could say it doesn't taste good or any number of contrived or unconventional reasons, and you'll still be made to refund.
Whether you accept the actual return or not of the product is up to you.
Sorry this happened to you. Why a buyer would purchase something of this dynamic without apparently having the slightest clue of what they were doing is beyond me, so I feel your pain there.
