Bad search engine optimization techniques can get you blacklisted from a search engine. Some techniques that are considered spam are cloaking, invisible text, tiny text, identical pages, doorway pages, refresh tags, link farms, filling comment tags with keyword phrases only, keyword phrases in the author tag, keyword density to high, mirror pages and mirror sites.
While these techniques might work to give you a higher ranking for short time in the long run they will hurt you.
Google has a good article on Google information for webmasters that is very imformative if you are considering Getting a SEO Company to so work on your website.