Recently, I invited a friend of mine to join this forum. After registering and confirming everything, his IP got immediately ban but he never use any VPN at all. So is there anything that he can do to get unban? I think he doesn't deserve to pay the fee so any help will be appreciated :-)
He must be using shared IP or his ISP allocated him IP (shared one) of another user that previously used bitcointalk for abuse so your friend also got ban.There's only 2 ways to life ban.Either pay the fee or ask your isp to allocate new ip/disconnect and reconnect router and then may be he can get new IP.After that clear cookies and cache and then ask your friend to create new account 
So he just have to contact his ISP to change his IP to another one and just clear everything and create a new account.
Thanks for the help
just pay fee it is some sat less than 1$
It isn't always less than $1.
IDK if these prices have been updated since the BTC price rise, but here's an interesting thread:
https://bitcointalksearch.org/topic/whitelist-my-nick-1396029
Basically, it also has a link to a post of theymos:
https://bitcointalksearch.org/topic/m.8044683
It seems to be possible to have 100+ units of evil, each unit of evil required a fee of 4023 sat. This means that some people will be asked to pay a fee of +402300 sat = 0.004023 BTC = +$20 at current preev rate
