Usually GST is only applicable only on new housing but not always. It seems a little bizarre but if the home you are buying had a business in it that may mean that GST is applicable.  GST is a business tax that really has nothing to do with what the buyer is going to do with the home after the sale. It has to do with how the seller used the property prior to selling it. If there was a small business like a water store or a hair salon running out of the house and it made a certain amount of money GST may be applicable on the sale. How do you know for sure. A prudent Realtor will put a clause in the offer that states  that, “The seller warrants that there was no commercial activity in the house that would cause GST to be applicable on the sale”. Realtors cannot give accounting or legal advice but they can protect you until you get some.