I get the concessions from the local MLS as well as the sale prices of the corresponding homes, find the percentage of the sale price that the concession represents, and then sort it based on closing date. Then you can get the median percentage fo...
The easiest (yeah right !) way would be to ask the agents when you are verifying each of the sales what they have seen concessions do over the past 12 months. I would focus on those agents who have the most for sale signs in your neighborhood.