When I was getting into this hobby (or back into this hobby depending on one's perspective), I confidentially asked this question to a well reviewed Kitchener based SP. She told me hardly any of her clients tip, and that it is the exception to get a tip - not the norm.
I tip about 50% of the time, but only with girls I repeat with. I've only tipped once on a first visit, and that was partly because she was new, 19, beautiful - and only charged me $100 for close to an hour.
From a client's perspective, they think $160 (on average) for an hour, that's about a day's wages to an average bloke. But what gets lost in translation is that the SP usually only receives about 60%, maybe $100 from the $160, with the agency collecting the rest. So I don't think tipping, at least 10% of the total, is unreasonable - especially if you want to repeat with the SP.
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