It is not illegal to sell landlocked property but lenders will not finance it. The buyer may pay cash or the seller can carry a loan. That is the easy part. The hard part is now the new buyer owns this property and he or she cannot get a loan financed on a house or outbuilding or other amenities to the property. When they go to sell it , no one but a cash buyer or seller financing again can buy it. The best thing to do is to either create a legal easement to allow ingress and egress or not take the listing or not sell it to your buyer. Make sure you read the Preliminary Title report to make sure you have access.