In Texas there are lot of new lands available for sale.So if you want to sell land in Arizona you have to advertise it well.
In my experience, it is 4% to 10% in a suburban area. It depends on how hard it is to sell. Vacant land in Manhattan may not need to pay any commission -- let the buyer pay it if they use an agent --...
A land with enough minerals can not be found easily.
You can find land at http://www.landseen.com/
Most of Minnesota's land was part of the Louisiana Purchase.