don't spread spam in SEO
Blog post how old and up-to-date the message. If the blog post is already two years ago, and a year and a half no new messages, rather abruptly springing a message, how much is a bit suspicious. If you are search for runescape money making guides, you can go to my online games blog to have a look.
Message correlation. Search engine by semantic analysis to determine whether the message and blog posts have some relevance. The garbage left by the mass software, usually does not make sense on where relevant, are not related.
Multiple blog comments modes. The bulk software will send spam to a large number of blogs, and remain the domain name and message are the same or similar content, this model will certainly arouse suspicion. I have 3 years experience on SEO. Once I committed to diablo 3 account sale. I usually write guides for d3 players about Diablo 3 accounts skills training and d3 gold making.
Spam characteristics listed above, there are some anti-spam software and search engines certainly have been used, but not necessarily all. And certainly there are other factors, we can not think, but the search engine think. The search engine is always smarter than we are.