Each person has 48 hours to respond to an offer/counter-offer. Maybe the seller was busy, or perhaps he was deciding and the time slipped by. Could be he thought your offer was a little low but didn't want to offend you with rejection.
You can make up to 3 offers before you have to buy it at full price or go without. Why not make a more appealing offer?
When you make an offer, the seller can accept, decline, ignore and let it expire, or make a counter-offer. If he accepts, it appears in your Purchase History and you pay for it the same as if you clicked 'buy'. If the offer is declined or expires, you can make a second (better) offer. If he counters, - then you can choose to accept, decline, ignore or make a further counter.
Most sellers are busy, and whilst there are a few that enjoy a good haggle, most make a counter-offer and that is about as low as they are willing to go. Unless the seller's listing invites haggling (I've seen the odd one that does) make the best offer you can and know that his counter-offer is what you can expect to pay. The following link outlines the process if you wish to have a look:
http://pages.ebay.ca/help/buy/best-offer.html
