To be honest you will more than likely never hear anything about what action, if any, eBay have decided to take against the seller for cancelling the sale without your consent. Even though they would more than likely make a note of your complaint if you reported the matter to them, and maybe even penalise the seller in some way for having reneged on the deal, I would be extremely surprised if they actually took the time to contact you and explain what action they took against the seller in relation to your complaint, as it would appear to be against eBay policy to do so.
Even though this is not exactly what you were hoping to hear, you can still leave negative feedback for the seller in relation to the transaction, even though he or she cancelled the sale without your consent. So long as you keep it simple and say something along the lines of "I won the auction but the seller cancelled the transaction without my consent, citing 'Buyer Asked To Cancel' as the reason why." Something along those lines would be more likely to stick on the seller's feedback record as eBay would probably not remove it if you had complained to them about the seller's actions, in which case any other potential buyers reading the seller's feedback from his or her buyers may well see the comment. If the feedback sticks then it could potentially do the seller far more damage in the long term, not only due to eBay hitting his or her account with a selling defect but also due to lost sales, in which case the seller's attempt to say that you asked to cancel the sale just so that he or she could avoid picking up a defect would ultimately have backfired badly.
