Determine your status: Are you a registered GST taxpayer? If no, GST is generally not applicable to the sale of personal household assets.
Determine the nature of the supply: Are you selling this as part of a business activity or as a one-off disposal of a personal asset?
Composite vs. Individual: If you are a business, identify whether you are selling a complete, integrated system (often taxed at 5% for the goods portion) or individual components (often 18%).