I think that's fine.
It's also fine to post negative reviews on your blog, although I would personally be careful to make sure it's warranted (one bad experience or problem not so much, persistent bad service or issues that cause a lot of problems and aren't quickly fixed would get a bad posting), and backed up ("I've been having problems with XYZ's inability to deliver products on time, and repeated wrong orders" vs "XYZ sucks!").