The fact that PMs from Newbies come with warnings, and you have to be at least full member before you can have an avatar mitigate the problem of impersonation to some extent.
We had a lot more impersonation scams before that newbie message was implemented.
That is true, but I've seen a couple of impersonation attempts where the impostor is bold enough to post in the original seller's thread trying to lure a user into sending them funds, so the Newbie warning message isn't shown. I think Operatr's idea of having a confirmed/verified account sounds like a good idea (much better than the idea I proposed earlier in this thread).