They don't post bad reviews. It would be...bad. For business.
http://www.reddit.com/r/Homebrewing/comments/2c53y4/i_emailed_midwest_about_issues_with_their_glass/
There are reviews that are not posted, and there are many reasons why.
We find that the 1 or 2 star reviews are upgraded to a higher score for that product after our customer service contact. It is possible that the product that was reviewed is not reflective of our entire line of that product. When we have resolved the issue, we encourage the customer to write another review (currently, we are unable to edit/change the original It is in the works though).
Other reviews are left by trolls with guest accounts, and no means to connect them to an order. We cannot allow reviews from people who have not purchased product.
There are also reviews that come in that are laden with profanity or vulgar comparisons. One of my favorites that couldnt be posted was a very positive one for a honey ale. The brewer made mention of some creative uses for the honey and the beer.
Any review that is submitted is read by our product team, and those reviews that contain negative feedback are also read by our President. We take them very seriously and it will drive changes for the better in homebrewing. Keep your eyes open, because we are trying to do a lot of things that brewers on forums are asking for.