I was just checking a thread and I accidently pressed "Buy Now" , but I didn't mean to, but then I couldn't cancel the bid, so i think adding "Cancel Bid" button would be good ay?
First of all, it gives you a confirmation dialog asking if you are sure you want to place a bid. As far as canceling a bid, you can't cancel a bid once you make it, only the seller can choose to reject a bid.