back in 2011 it was very different from now on maybe you could have 1000 accounts for this forum ... and when you return in 2017 the forum is getting full, account sales may still be possible ... and for now many police in this forum are looking for twitter links, ?
Quite a lot... have a look here:
https://bitcointalk.org/index.php?board=129.0Particularly in this thread:
https://bitcointalk.org/index.php?topic=2544574.0Twitter, Facebook, ETH addresses, BTC addresses... you name, they'll use it to link all your alt accounts and get them all tagged.
Alt accounts are not "prohibited" per se... but being an alt account of a BANNED account is likely to result in being tagged. Likewise, while account sales are not prohibited, they are frowned upon by a number of "Default Trust" users as they usually lead to spamming and/or scams... and again, are likely to result in being tagged.