Most of the time many SEO expert here tell to improve your site do the unique and quality. I wondering is there any tools like google toolsbar PR that tell me my content before post is unique and quality enough? I don't know all the10,000 firefox add-ons, did I miss any toos to check my content before post? It may be stupid but I think I had better ask here which the most biggest community on seo that I know on the planet.
Use copyscape to check your content....apart from that u can just google with your content to know if its unique
copyscape.com will show u if someone is using article like u. or write few lines in any search engine, if it will not unique u will see other articles will appear in SE
As for the quality, that is more for your users. The better quality your content, the longer users will stay and the more likely they will be to link to your website. The search engines aren't smart enough to tell if content is high quality or not. The best way to ensure your content is unique is to write it yourself. If you use freelance writers you should check to see if they stole the content. I usually take a random sentence and search for it in google enclosed in quotes. I have hired a freelance writer who stole an article and claimed he wrote it.