Sell Happy Card - Retail Therapy gift cards on the GCX gift card marketplace. Happy Card - Retail Therapy gift cards sell the fastest when discounted between 2% and 20%, but the asking price is up to you. When you sell unwanted gift cards, we'll send you cash back to use at other stores. Check to see if your Happy Card - Retail Therapy gift card expires, and simply enter the retailer's information below on the GCX Sell Gift Card form.