I can't remember using at market with commsec iress.
I'd place a sell lower than the bid and commsec matched the best price, it's stated in their trading conditions document. So they sell into the bids for you from the best bid price until it hits your sell price.
That always worked for me.
If you are finding yourself at the top of spike and really want out then I suspect that you are approaching trading all wrong and will soon lose your capital.
