I just purchased an expensive (for me, anyway) bub from a relatively new member. I did exactly this ^^ and still didn't feel comfortable pulling the trigger. So I went one step further and read through the seller's posts to get a better idea of the member's "true colors" as it were. After reading through a half dozen random posts, I felt much more comfortable as it was clear to me that the guy is a true vaporist and knew his stuff.
So the only thing I would add to the above list is to randomly sample some posts from the buyer. It helped me feel confident to pull the trigger and I'm now loving my new Mobius ion.
edit: Oops... I didn't read vtac's 3rd bullet right the first time.