I thought the evil fee was not introduced because of knowledge gaining, else it would have been called a registration fee and made compulsory.
Most real users don't have a problem with evil fees. I can just create a new account from my own IP address without problems, but if I use Tor, I have to pay the maximum.Quote from: theymos
You may get the impression from complaints on the forum that everyone hits the fee and it's never warranted, but this is selection bias: the fee is more rare, and the vast majority of accounts that hit it should not be whitelisted.
From personal experience I know very well that 2 of my friends gave up registering and participating in this forum due to evil fee.
I'll try again: ask them to join again 
Tell them not to take it personally, and I'll happily whitelist them.Quote
because they accidentally used the same IP
It's not only the exact IP, also the ones "around it" that get collect units of evil.Quote
I think that another way should be found to prevent the registration of possible scammers on this forum.
That's not even the goal, scamming is allowed. It's spammers that get banned and cause evil on IPs.I've whitelisted 26 users in 6 weeks. Two of them have earned a lot of Merit already, none of them have been banned yet. I can't possibly know if they're ban evaders, but I've rejected many times more requests than I've accepted.
In addition to limiting by IP address, it is quite possible to calculate the number of your users through browser fingerprints.
See:A year or two ago I was researching fingerprinting techniques that'd work against pretty much anyone with JavaScript enabled, and I found several promising leads on that front. But then it occurred to me that I don't really want bitcointalk.org to be known as the #1 forum on the leading edge of de-anonymization technology, so I stopped pursuing it seriously...