I understand why you would be nervous about not getting a response from a seller, but I buy on Ebay all the time and just started selling, and it is common to first ask if you can pay at a later date and then bid. It seems a bit passive-aggressive to first ask to pay late and then leave a negative because the response wasn't fast enough. You were the one who broke the agreement by not paying once you won, especially since the seller didn't agree to late payment beforehand.
I only leave negatives if the item is significantly not as described and the seller is being incredibly difficult about admitting it or taking it back, and in hundreds of transactions have only done it twice.