Have you ever hired a freelancer to do design work? Did you have a clear idea of what you were looking for, or only a vague notion of what's good and bad?

I fall under "yes and the latter". I recently hired a logo designer on eLance and I feel like good communication can make the difference between a mediocre and a great final design. But I'm not super-good at articulating what I like/dislike about an iteration and feel unhelpful giving feedback like "this logo doesn't feel right".

So I figure some of you out there must have been in my position before, perhaps they even learned a few things from the experience. Maybe you can share some wisdom or point me to a good article on the subject? It will be greatly appreciated :)

Thanks!