Here's a little anecdote about letters from official sources...
About ten years ago my father was treasurer of the local curling club, and we had a 96 team bonspeil that brought in a fair bit of revenue through entry fees. Concerned about the GST, he wrote a letter to Revenue Canada asking their policy in these situations.
In return, spaced about 3 weeks apart, he received two letters from two different people in the tax department. One stated that the GST must be collected on bonspeil entry fees and submitted to Revenue Canada. And ...you guessed it... one stated that the GST need not be collected or submitted as regards entry fees. Both letters did contain the caveat that the final decision on the subject would be provided by the auditor or courts should it come to that, and the letter was only intended to provide guidance.
Needless to say I don't put much stock in official letters anymore, as they're nothing more than one person's interpretation on any given day, and apparently that interpretation is absolutely meaningless.