I've done moderating work when phpbb forums had their heydey. The clever sockpuppet accounts or voting rings don't start posting about the projects of their main account right from the first day. The clever ones remain dormant, mostly idle, participating in other discussions. They look just like normal accounts.
But much much later when the main account posts a "show project" post, the sockpuppets or voting rings add +1 or post a few words of praise and then move on to commenting on +1-ing other posts.
And voting rings become more difficult to detect when they don't post anything related, post unrelated stuff but quietly upvote the main account's posts/comments.