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If a user subscribes to their feed through My Yahoo!, Bloglines, or some other service, these sites will grab the actual feed, and then serve it to the user. This is fine. But, at least with Yahoo, those feeds are automatically put in their database. Then some other person could search for BrandX, find the feed, and publish it in their blog. If it's a really good deal, and the feed becomes popular, then that product has the potential to rank in the SE. Is there anyway to tell Yahoo, et al, that they can retrieve this feed, but don't allow it to show up in a search?
Disclaimer: I know, highly theoretical and unlikely situation, but it's something that has to be considered.
The question that would arise is whether someone added it to myYahoo would Yahoo kind of ignore the robots.txt and include it in their index because one of their members asked for it.
A good question. Don't know the answer.
However, this really goes against the whole reason for RSS. RSS is an open syndication model. If you have articles you don't want in your feed you would not add those to your feed. What you have to do is make a feed of ONLY the articles you want syndicated.