The exact number of hobbyists is always going to be a mystery. But I would assume that repeat customers of escorts or spa girls would sooner or later find TERB and stay for the reviews.
I found the boards back in the early days of the Net and I had no special expertise in finding resources online back then. I simply looked at escort ads and websites and there were references to TERB that I went to check out.
So I would assume that the guys who DON'T know about TERB are the dudes who see escorts 2x a year when the wife and kids to visit the in laws for a week and are too scared the rest of the time. But even then, seeing escorts is addictive for a first time customer. When I first booked an escort, it was "Well, I'll just do this once to see what it's like..... "
The old TERB published the # of members and it was close to 200,000. Now that is since 2001 and most of those accounts are dormant. But it still represents an average of 900 new members a month. And assuming those members stay active for 2 years, 21,600 active members, incl lurkers at any given time.
Your absolutely right the exact number of hobbyist will never be known.
I think the very high majority of hobbyist that sees SP’s or MPA’s in 2020 and has done so more than occasionally reads or contributes to this review board or another.
It's just the nature of how business in all industries are conducted these days and how customers find reliable businesses or in this case SP’s to book.
I stumbled upon TERB by accident back in 2010 and not a single person that I knew who visited massage parlours or escorts back then knew about TERB. Now in 2020 I have multiple friends who are on TERB but they rarely or do not post at all as they are lurkers, they read and observe information from the reviews and avoid the bad SP’s and book the good ones.
Point is large percentage of TERB members are lurkers and they represent a large percentage of customers.
Whether they ever admit to knowing about TERB to SP’s is another subject.
Very few SP’s know I am a TERB member.