"Customary" can varie...the size of the acreage shouldn't matter that much, as it is based on a %, usually, it could actually be a flat fee, but that is less common. Land listings could be a range of 5-10%....
What type of land is it? Just curious what kind of buyer you might be looking for. Is this a buildable lot? I would be happy to talk with you further about this, feel free to give me a call..I am not that far away!
I hope to hear from you...