One thing you could consider, especially if the owner is giving misleading information to prospective buyers, is to get a lawyer to send a letter telling them to desist or you may take action against them if they interfere with or impede your selling campaign in any way. That usually scares them off, and is worth the small investment.
Very short-sighted really, the higher the price you get, the more their place is worth, plus they are getting rid of you!