all good and true...with respect to your first sentence then, an escort should file under personal "health service provider" just to be exempt from GST (if this is possible). LOL, there's gonna be a lot of massage therapists out there!
but the fact remains that the money earned from the escort business is mainly "under the table". the fact that the escort "should" comply with tax laws does not mean that he/she WILL. under reporting one's revenue is also possible (and of course highly illegal). i do not believe that every single escort does their income tax return properly, or pay their share of taxes. i agree with what you are trying to say here, but it is difficult to prove that an escort actually made X dollars because there is no paper trail (unless the escort actually logs the client and keeps track of revenue). as long as the escort's income tax filing is fairly consistent from year to year without any large "swings" that would raise warning bells at Revenue Canada, their return gets buried along with the rest of us.
but back to the original point: if the escort does make over $30K in revenue, it would in fact be better that the escort be either incorporated or proprietorship. Anything to put the escort into a lower tax bracket is preferable. In either scenario, GST would be due and payable (unless the escort is exempt due to being a health service provider as you mentioned). if GST is payable, it would be in the escort's best interest to file quarterly (IMHO). Annual filing, while allowable by Revenue Canada, may cause some problems for escorts with poor cash management abilities. Being stuck with a large GST bill at the end of year will financially "kill" some SPs. Paying quarterly may be the only option for them to budget for the quarterly pmt. My 2 cents.