PayPal Digital Gifts is selling Southwest gift cards on eBay that can get you a decent discount. You will pay $135 for a $150 gift card, which gives you a discount of 10%. These purchases no longer qualify for 5X, but you can earn at least 2X in credit card rewards.
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Purchases are limited to 5 per buyer
This sale gives you a 10% discount. It’s probably not worth purchasing for resale but could be a good idea if you have any paid Southwest flights coming up. You could also try a shopping portal, but I think none of them has worked in a while for gift card purchases on eBay.