My client was a corporation provided consulting services to a company in the US. It was audited by the CRA. The auditor did not understand the GST/HST rules very well. She proposed to assess the corporation for not collecting HST on its revenues, because the "place of supply" of its services was in Canada.
I explained to the auditor that, although the "place of supply" of the services was indeed in Canada, the zero-rating rules took precedence and meant that the services were taxed at 0%, so no HST was collectible. I insisted that she review this issue with her GST/HST Technical Advisor.
The auditor agreed and cancelled the proposed assessment.