Does my grandson have legal claim to my property?

My grandson is trying to force me to sell him a piece of property. I allowed him to move his trailer on four years ago, and he had to put in a septic tank and drill a well. He knew that before he moved on to the property. He had a lawyer send me a letter stating we had a verbal agreement to sell him the property for $4000. I did at that time offer it to him but he said he couldn't afford it. There is no lease. I have wanted him to move but he won't. He is a nuisance. He hasn't helped me in any way. He does what he wants without permission and to other people's property. I have gotten two offers to sell it for $10,000. Does he have a legal claim to my property?