What to do if I sold a painting to a client 6 smonths ago and the client has not picked up the piece?

Based on your question I assume that the customer paid you for the painting, and that you expected the customer to pick up the painting; the customer did not pick it up; the customer asked you to refund of the money that he previously paid for the painting; and you refused to give a refund.  Since you have been paid, the customer owns the painting.  Under the circumstances it would be best if the customer had possession of the painting.  Since he has failed to pick it up, I suggest that you ship it to him, along with a letter saying that the transaction for the sale of the painting was complete when payment was made, and it is not your policy to give refunds or accept returns after a purchase has been made.

I suggest that you