My forum is subscription only, and (every)one has to register, first, no anonymous entries.
They then do not become a ‘member’(group) yet, and can only see one category, which only directs them to the ‘welcome’ and the subscription page. About half stay there and never subscribe for whatever reason.
Only once subscribed do they become part of the ‘member’ group and can see all the other categories and within 10 minutes of reading get Trust Level 2, so we are all on an even plane.
This works quite well. I have one per month subscription product and one per year subscription product.
Unsure when someone stops paying/cancels the subscription if they automagically unbecome members, so I keep an eye out myself to do this by hand, the forum is small enough to do this. Once they subscribe again, for a month for instance, it does put them in the member group again (should at least 
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