SEO tricks are over optimization in googles eyes. That is exactly why people over optimize. We try to "trick" google into giving us a higher ranking.
Redirects - Acquiring related websites to redirect to your site would be a method to try to manipulate your search engine rankings. Why else would one do it? The proper thing would probably be to keep that website as its own entity and develop it on its own.
3. Aggressive link building. Why else would someone buy links with the same anchor over and over? They are trying to rank high for that phrase. They are paying money for these high PR links, so why would they waste their money and not use their money term as the anchor text? They are trying to "trick" google into giving them a higher ranking.
We are all trying to trick google in some way. Every single person on this forum is here to try to find out more information so we can better trick google. The person who puts up a website with no page title, no seo friendly URL's, no meta description etc, that's the guy that's building only for his audience.
You can call them what you will...there is no standard set of rules for what qualifies as over optimization. These are potential factors that may cause your website to lose rankings.
There is a fine line between optimizing and over optimizing. Nobody knows where that line is but google. Every time we make a change to our websites, we are optimizing in some way or another.