I sell online as a small business and Digeroo, Amazon has a very hard and fast rule that bad feedback left for a seller which is in reality a product review ("poor quality item", "not fit for purpose" etc) is removable. So try writing a product review.
And I've seen loads of 1 star product reviews which mention the seller by name .....
Websites do have funny rules though sometimes. I had a product review on Tesco Direct rejected because it mentioned the price I'd paid - they allow you to say you bought it on offer but not the price you paid. But Amazon doesn't seem to bother about this.
And you have to be a bit careful with ebays's basket: if you are storing stuff in there for later and then hit Buy It Now on something else, ebay trys to add your basket items to the item you are purchasing. And it's easy to miss. But if you buy in error or just found it cheaper elsewhere, you don't have to get het up, just tell the seller you want to cancel the transaction and the seller will send you a cancellation, then they can get their ebay fees refunded - currently 11% of the sale incl P&P charge. We are just businesses and don't want to waste time when someone won't be paying anyway.