I do not believe you can promote a product by saying things like "buy this" or "this is the best product around." Things along that line where you are clearly advertising that product and putting many links to it are not allowed. You are allowed to review the product or give information on it. You can say why it is good, but you can't be too biased. In a sense you can promote a product by making people aware of what it is and what it is used for, but you can't promote a product by posting advertisements.
I hope this helped.