A makeup swap is when you swap an item that you have with someone else in exchange for an item they have. No money is exchanged. A makeup sale is you selling your makeup. You can sell or swap your used foundations. You just have to create a post describing, the items, usage and price. Pictures are also helpful. You will need to provide some sort of feedback to prove you are reliable such as eBay feedback or makeupalley feedback. Hope this helps and good luck with your sale/swap.