eBay fraud

I purchased items on two separate ebay auctions and paid the seller who lives in Canada. I won them for low price and they are worth thousands more than I paid. A few days after I paid the seller refunded my payment stating that she found out the items are worth much more and she will not sell them to me. Isn't an ebay sale a binding contract and isn't it fraud not to mail me the won items. Although she refunded my payment, it is like she is stealing the value of the items from me.