The bulletin also provided guidance on certain common mistakes to avoid. This includes charging and accounting for GST on the net difference for trade-in goods, which is incorrect. For example, if a customer trades in an old computer for SGD 300 when buying a new computer for SGD 1,000, GST should be charged on the full SGD 1,000 and not the SGD 700 net difference. Further, if the customer is a GST-registered business, the customer should charge and account for GST on the trade-in value of SGD 300.
Another common mistake is not charging GST on inter-company transactions. The bulletin clarifies that GST is a broad-based consumption tax levied on all local supplies of goods and services, including inter-company transactions.
Source Orbitax