t Hello,My name is XXXXX XXXXX I am a US lawyer.If your neighbor does not respond favorably to your letter, then you will have to take legal action. You could contact a lawyer and have him file or threaten to file a lis pendens against the property. That is formal notice that you intend to sue to resolve a legal problem involving the property.While a lis pendens won't prevent the sale from going through, it does warn prospective buyers that there's a dispute regarding the property. As you can imagine, learning of this can be very discouraging to a potential buyer. So it may make the owner more eager to resolve this problem with you than he is right now.If you don't know where to find a NYS property lawyer, you can contact the New York State Bar Association's Lawyer Referral Service. They charge a fee of around $35 for the referral but it includes a half hour free consultation with the lawyer that you can have over the telephone.