E-commerce Insights: The (Free) Benefits of Google’s Webmaster Central

Providing duplicate content to Google dilutes your page rank, leading to lower placement on search results pages and reduced sales.

Use a free tool like Web-sniffer.net to ensure your server is handing out 301 permanent redirects, not temporary 302 or 307 redirects. Again, while this small detail sounds obscure, it can have a substantial sales dollar impact.