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%. Keep in mind that you’re no longer earn 5X on these purchases (unless you still have an Ink Mastercard) so use any credit card that will give you at least 2X in rewards.
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Purchases are limited to 5 per buyer
Not a profitable deal for resale but could be useful for personal use. If you have an Ink Mastercard then you can probably get very cheap Ultimate Rewards points.