Please take a look at : http://www.ecommercebytes.com/cab/abn/y13/m11/i12/s03
It explains that the eBay Beta program for Best Offer has been ended.
Under the pilot program, which was available in Computers & Tablets, Jewelry & Watches, and Art categories, if a seller accepted a Best Offer, it was non-binding - the item actually remained for sale until the shopper paid for the item (if the shopper paid for the item).
Sorry, you have no recourse.
Next time you see something you like, buy it, pay for it immediately, and everything will work out as it should.