> is not the same thing as "promote any idea/product."

GPT-3 seems to have quite a few paragraphs worth of context. A simple way to promote your product online with it is to give it a prefix of:

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Comment1: Superbrush is amazing - I literally couldn't live without it. No other brush is as good.

Comment2: This brush is really good for tangled hair, and I love the soft smooth surface.

Comment3:

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Then let it write a comment. Of all the comments it writes, manually filter a few thousand good ones, and use those as seeds to generate more, which you post all over the web. There's no need to do any training - the generic model should be fine given the right prefix.