Got Sick Last Night & Didn't Get This Post Up: Clients and Competitors

Wasn't feeling great last night, but I went to bed with a blog post in mind.

I wanted to talk about blogging on clients' competitor. One of my clients that has yet to launch has a competitor in the space that I'm actually interested in trying. I worry about the ethically issues. If I try it out and write about it--regardless of what I say, there's the possibility of it being taken all wrong and coming back to me in that light. If I right something positive, then I've given a competitor publicity. If I right something negative, it looks like Astroturf.

So clearly, I haven't written about this topic yet. What do you think? Can I review a product or service on my blog knowing it's a client's competitor?