IMO, the concept that every Service Provider we encounter through our day should be tipped is nonsensical. There are time, places and people to tip - and not to tip.
I tip generously to those Service Providers that rely upon tips to make a living wage - wait staff, house cleaners, dog groomers, garbage collectors, hair stylist, etc...
I'm a little (lot) less inclined to tip those whose hourly wage dwarfs many highly paid professionals; like, I don't tip my doctor or my lawyer. Yes, they provide an essential service, but they make a good living on their billing rates. For example, a lawyer bills $100 to 495/hr on average in the US:
https://www.contractscounsel.com/b/how-much-do-lawyers-cost
Now, this may be a stretch for some, but if I don't tip the guy/gal who saves my life medically or legally because they already bill to make themselves a good living, how do I justify paying an escort a tip on top of a "hundreds-of-dollars-per-hour" billing rate? In my area, most are billing more than the lawyers do.
Sounds like I'd never tip an escort, eh? No... there is an element of relationship and intimacy that I recognize. In general, I think repeat business is the best gratuity. In cases where we have developed that relationship and intimacy to a certain level, I may tip or offer a gift. When I do, it is proportional to what I might tip any other service provider; for example, I do not let my penis tell me to tip 100%!
An aside: I always tip an agency provider.
In the end, what you do is up to you - there is NO "RULE" and NO "NORM".