We don't allow private messages before the task is assigned, to give all members the same opportunities. We encourage this fairness and open honesty at all stages of the Airtasker journey, to maintain an authenthic marketplace.
The comments section on a task allows for public negotiations and discussions about the task.
Just click on the task you are interested in, scroll down to the comments and start talking. The comments will be visible to everyone until the task has been assigned to you.
Although your comments will be public, your offer is only visible to you and the Poster. This way there is no undercutting and everyone is on the same playing field.