Sounds like you're using a discount broker. Bit like getting H & R Block to do your tax.
You might be saving $20 on brokerage but it's probably costing you thousands in poor execution and not having the tools of trade.
I think you are firstly getting confused between Centrepoint and Chi-X. Centrepoint is trading between the pips. If the stock is 1.3c and you bid 1.4c and there is sellers at 1.35c in the dark pool (Centrepoint is a dark pool market) then you will get that price. Same the other way around.
Most discount brokers as far as I know don't let clients bid or offer on CP because it is a day only market and requires more work therefore more cost. They are really only aimed at the Mum's and Dad's.
Chi-X is another exchange. To confuse things you can bid on CP either through Trade Match (ASX) or Chi-X. Again, Chi-X is a day only market and again the discount brokers generally don't allow you to trade on it. This means that you can miss volume.
Given the discount brokers generally use the ASX feed you don't get total volume of the day (both Trade Match and Chi-X).
Hope this helps you out.
Malio
MRD Price at posting:
1.4¢ Sentiment: Buy Disclosure: Held