If the shacks have occupancy permits I would keep them. It they don't, tear them down.
If they are occupancy permits, then a buyer will have a much easier time obtaining financing.
Without them, the listing would be for vacant land, and there are tighter restrictions and fewer lenders that will lend on vacant land.
A large number of the investors I work with look for properties with "junky" but habitable structures so that they can rent them or write off the property as a second home. (Speak with a tax professional for details)
Also, vacant land is tougher to finance than property with homes.
I recently was involved in a transaction with a property that had a shabby home on it and when the final negotiation came through it was for the price of the property minus the cost of removing the structure.
Now, if you meant that there are literally two shacks on it then that's a different story.