In a nutshell free blogs from and being free hosted by wordpress.COM cannot be used to drive traffic to third-party sites by means of advertising and/or affiliate programs (see next section for more clarity). E-commerce tranactions via shopping carts and the like cannot be conducted on wordpress.COM blogs. No retailing or reselling the work created or services provided by anyone other than yourself is allowed.
Affiliate marketing blogs
The only exceptions with regard to affiliate links are found here:
Affiliate marketing blogs: Blogs with the primary purpose of driving traffic to affiliate programs and get-rich-quick schemes (“Make six figures from home!!”, “20 easy steps to top profits!!”, etc). This includes multi-level marketing (MLM) blogs and pyramid schemes. To be clear, people writing their own original book, movie or game reviews and linking them to Amazon, or people linking to their own products on Etsy do NOT fall into this category. http://en.wordpress.com/types-of-blogs/
I am sorry, but advertising is not allowed on free hosted WordPress.com blogs. The only exceptions are for high traffic blogs that qualify for and are accepted into the Ad Control program, and very high traffic blogs that qualify and are accepted into the paid VIP hosting program.
If you require an ecommerce site, advertising and/or affiliate links on your blog, you can hire a web host and get a free software install from http://wordpress.org In that case, please see the information at the link below to learn about the differences between free hosted WordPress.com blogs and WordPress.org software installs for self hosting. http://support.wordpress.com/com-vs-org/
re:duplicate content blogs
Duplicate content blogs are not allowed here at wordpress.com. This is what Google has to say.
However, in some cases, content is deliberately duplicated across domains in an attempt to manipulate search engine rankings or win more traffic. Deceptive practices like this can result in a poor user experience, when a visitor sees substantially the same content repeated within a set of search results.
Google tries hard to index and show pages with distinct information. This filtering means, for instance, that if your site has a "regular" and "printer" version of each article, and neither of these is blocked with a noindex meta tag, we'll choose one of them to list. In the rare cases in which Google perceives that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved. As a result, the ranking of the site may suffer, or the site might be removed entirely from the Google index, in which case it will no longer appear in search results.
Click through to read the complete entry http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=66359