So it's been on for 3years and plenty of houses have pulled good...

So it's been on for 3years and plenty of houses have pulled good prices in that time. Must be a good reason it hasn't sold. That's worth keeping in the back of your mind when thinking of the re-sale value.
They've hung on for 3+ years, if you haven't already, try to get some info from the agent, how old they are, why they are selling, how long they have had it etc. I would assume they are sick of it by now and are keen to move on. Don't underestimate what impact recent media about the current financial situation and Australian housing market could have on the mind set of someone in their situation.
And good luck!