The price a property achieves tends to degrade the longer it is "on the market". Avoid the temptation to allow lots of 'negotiating room' - you may find you miss buyers completely and end up chasing the inevitable declining price with a lower price eventually achieved much further down the track.
What negotiating room should I allow?
Accurate pricing is important for a successful sale. Todays buyer is sophisticated and has plenty of market data available to them when assessing the value of your property.