eBay seller refuses to sell a "Buy Now" item

On Feb 11th, 2009 I found a "Buy Now" offer for a computer component from a reputable seller for only $9.99 each. I proceeded to make a purchase of two. Later I reasoned that it was such a wonderful offer that I returned and proceeded to purchased two more.

I later received an e-invoice, confirmation from the seller on my purchase, as well as a receipt of funds received for the purchases.

That evening the seller email me directly outside of the eBay norm and informs me that they cannot honor the transaction since they made a mistake on the pricing. They mention that the price for each item is actually $49.99 and not the $9.99 that I payed.

They then inform me that they apologize for the human error, promise to give me a gift next time that I buy from them, and mention that they will be refunding my purchase amount shortly.

My questions here are:

Where is the sellers responsibility on assuring that their items are properly priced and posted?

Where is the enforcement of "legal binding contract"?

What are my options here?

To what extent will eBay/Paypal go to enforce their so call "Fair Trade and Practice Policy"?

Please advice.

Joey

In a shop or market stall, items may be displayed as an 'invitation to treat" and not actually be for sale; it does not even have to bear a price tag at all; this is perfectly legal. But it is misleading to put a low price tag on something you have no intention of selling at that low price. If a seller does so, there should be displayed at the trading place something detailing the justification - example, if bought with another item, or in multiples, or whatever policy the seller may choose. It is not appropriate to contract in a sale (and, by confirming a 'Buy It Now' option, this stands as an agreement in contractual law - you agreeing to offer money, the seller agreeing at that instant to provide an article in consideration of that offer) and then retract it and demand a higher price. Whether or not the mistake by the seller was a genuine one, the acceptance still stands as the contract of agreement. Now, a contract can be broken with the possibility of damages on either side - which could be the difference in replacement cost of the same item that you were forced to purchase elsewhere - plus associated costs, if any. A small claims procedure will likely serve you well if you are stonewalled by the seller.