Trade site question for new player

Someone told me I can't "bargain" on items in the trade site. Is this accurate? I asked someone to sell for 8c instead of 10c because others were selling for 5c but they were offline. Is this not allowed in game?

So long as you have not altered the original trade message (I would like to buy your wotsit for 10 chaos etc), and the person has then sent you a party invite/trade request etc, you can ask them via message if they are willing to sell for a lower price. Some may, many will not. As long as you ask politely, it should not be a problem. I have sold things for less when asked :)