The answers to your question range from fairly good but incomplete to 'where is your head?' Most used items are sold "as is, where is", unless the buyer can prove purposeful deception. You did not purposefully deceive the buyer, so legally you owe him nothing. If he does take you to court: 1) make sure you bring the texts, emails, or? to prove that you offered him a full refund. 2) make sure your side of the transaction is as documented and consistent as possible. 3) Go into court with the confidence that you offered to make it right, even though you have no legal obligation to do so (if you can say to the judge, " the refund offer is still valid, if the plaintiff wants it (and a full refund of $60 is ALL he could ever collect; no court costs, no aggravation, no loss of pay, NOTHING ELSE).
Call his bluff: he will lay out far more in costs than he could possibly recover. If you want to be generous (legally you don't have to be) offer him the refund again (of course on terms that you can afford; $10/week or whatever).