I just looked at my invoice and see many of these lines called: "Store Referral Credit" with the negative sign to them. It surprised me at first so I looked it up and see that eBay actually refunds 75% of my FVF if the buyer came from outside of eBay. But I did not advertise my eBay store anywhere, I have my own off-eBay store!
I am thinking how this happened and finally came to this theory. If my eBay listing ranks well in organic search on Google/Yahoo, I get a store credit!!!
Why I am so excited, you may ask. Well, eBay is one of the best ranking sites on internet. Add a good keyword and combination eBay's rank and your dead-on keyword will bring your eBay listing way up in the organic searches. Add a cherry in a form of 75% discount and you see why I am so excited about this finding!