Most everyone I’ve talked to about allowing product reviews on their site or comments on their blog expresses the same fear “what if people write negative comments?”.
I’d suggest a read of Andy Beal’s Marketing Pilgrim post of 5 ways that negative reviews can help your site.

The upshot – comments are an opportunity to improve and they lend a little more credibility to all the glowing reviews that are on your site. You can’t please everyone, but you can please the people who matter – your target customer. Andy quoted Andrew Goodman:

“I was recently a little disconcerted when I visited the American Apparel site, because of the presence of too many glowing, cheerleading reviews of its products. Some simply said “I haven’t tried this yet but I’ll be getting one really soon!” Poring over the various reviews, I actually felt like I’d be more likely to buy the product that had at least one negative or moderate review. Why? Because I wouldn’t be as likely to suspect that the reviews are fake.”

I think this is a more true statement than people realize. I know that when I look at restaurant or movie reviews, I look for things in them that I care about and I take all positive and negative reviews with a grain of salt… No two people are the same and things that some people hate are things that I love. For example, if someone writes: “the food is too spicy!” guess what? I LOVE it when my food hurts and makes me sweat!