Hi My Linh

As far I know the Search Engine rankings issues are absolutly not so technical as claimed here, even Google have implemented several Spam filters. If you are starting to rewrite your URL's, please consider following:
1. Do you research and rename your files with appropriate keywords inside. It does not matter, if you are using "-" or "_" between words, even claimed by some experts sometimes.
2. Use appripriate anchor text (e.q. text inside the link).
3. Try to match those with the content in your page and search phrases used to search particular item.
If you want, I can research some search terms for you using trellian?

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