I responded as requested.
Lauda, thanks a lot for the reply! Now I realize that there's not enough evidence for BTCtalk accs connected with similar twitter accs. The bounty abuser could just use random forum profile links to fill user link field, because there's no verification requirement for them (if they had to PM manager on forum for example to get approved, this could work). Indeed a big research on these accs needed to proove them as 1 big bounty farm.
Most social media bounty campaigns doesn't verify forum accounts and (if the specific campaign has for example Member+ participation rule) it's easy to bypass the rules by simply using random user profile link...