GST is essentially tax only on commercial transactions. Hence only those supplies that are in the course or furtherance of business qualify as Supply under GST. Hence any supplies made by an individual in his personal capacity do not come under the ambit of GST unless they fall within the definition of business as defined in the Act.
CBEC vide press release dated 13.07.2017 has clarified that sale of old gold jewellery by an individual to a jeweller will not constitute supply as the same cannot be said to be in the course or furtherance of business of the individual. Sale of goods or service even as a vocation is a supply under GST. Therefore, even if a famous politician paints paintings for charity and sells the paintings even as a one-time occurrence, the sale would constitute Supply.
However, there is one exception to this ‘Course or Furtherance of Business’ rule i.e., import of services for a consideration.
Source: CBIC Website