Once a buyer offers you a price that you're willing to accept, start the process of arranging a meet up. There is no formal way to accept, just let them know you're interested in their offer. Find out when you're both free to check out the item and then make the exchange!
If you change your mind and decide not sell the item (or, to sell to someone else), you are allowed do so. We recommend communicating any changes of plans as they occur, however.
