Posting ads for your item or buy gw2 gold for your website is just rude. They will likely be removed by the weblog or group forum administrator as will you be removed from the membership record. Advertisements are generally banned from all weblog and group forum sites.
What can and should do is consist of your website deal with in your trademark tag. That is not considered advertisement. It is a aspect of your identity and is viewed as such by the administrators as well as the members of weblogs and group forums.
Remember that your content need to be thoughtful, considerate and employed to other members and must never EVER appear to be ads for your website or for your items. You can recommend your items as solutions for problems within your content but they must not look like ads. They must appear to be of the "friend-helping-a-friend" variety.
Never consist of hyperlinks to your website within the body of your content to weblogs and group forums. This can be construed as marketing and it can get you tossed out on your ear. You must be satisfied with the hyperlink to your website that will appear just below you name in your trademark tag at the end of each publish.