After contracting to purchase land and buildings already. Seller may not cause any building or land to sell, so the increased obligation occurs, your guests will buy.
After a contract to sell the land and building. Seller shall not commit any act whereby the land and buildings to sell the resulting increase in the obligation to buy.
After the contract for the sale of land and buildings. The seller must not any action, which is why the land and buildings to sell is increased to the commitments to purchase.