Boardwalk - Federal Court of Appeal appears to find that form of invoice drives the substantive GST result

Under an Alberta government program to defray high energy costs, a supplier of natural gas to Boardwalk would charge Boardwalk the full price of, say, $100 plus GST of $7 thereon, and on the same invoice show a credit for the amount of the government grant of, say, $20 that would be received by the supplier from the government on the due date of the invoice.

In these circumstances, Webb JA found that GST was payable by Boardwalk on the full $100.  He reasoned that the supplier did not accept the government grant as a partial payment of the consideration until the subsequent due date for the invoice, i.e., after the GST had already been triggered on the invoice date.

This seems to suggest that if the supplier had instead simply charged GST on the ($80) net amount (implying that it was taking on the slight risk of not subsequently receiving the $20 grant), Boardwalk's GST liability would have been reduced to $5.60.

Neal Armstrong.  Summary of Boardwalk Equities Inc. v. The Queen, 2013 FCA 140 under ETA - s. 123(1) - consideration.