Many companies are using blogs to promote their product, some have been successful and some others have burnt their hands. The reason being that a blog once initiated, remains no longer in control of an individual person or a company. As opinions of visitors start pouring in, the blog develops an identity of its own.
Successful companies take a deft & ethical approach to the blog. Some ground rules: negative comments are to be thanked for as feedback on the blog, no comment should be deleted or rephrased. The company may contact the blogger and request him to moderate his comments if they are unduly harsh. Never try to rig the blog by faking the users and comments (known as flog), as the blogging community will realise it in no time and the negative news travels faster on internet. The negative publicity then gathered can permanently damage a company's reputation. There will be some blogs out there whose topic will be relavant to the company product. For instance a company launching a beauty product may find blogs on beauty tips. A company should visit such blogs and give relevant comments (as the company, no faking again) and leave their blog address for bloggers to click and follow to the company blog. Similar strategy may be followed with the experts on the said product line who maintain their blog. Taking the same example, blogging on the blog of a beauty expert will oblige him to reply and comment on the company blog.
A blog is very transparent world on internet and a honest, ethical and strategic approach can yield positve results at literally no marketing cost. One last comment, if the product itself is bad, dont blame the blogging community. Bad news travel faster and in no time the company will know that on its blog, much before the market research team informs the same.