I prefer emails to PMs since I will just get a message I can reply to on my phone. But I do not go as far as to shun the PM system here...
Also, if I am going to buy I seal the deal quick or walk away. So there is not a lot of back and forth. By the time it hits "email me" phase it is to get the tracking number.
But as always, if you are not 100% comfortable with a deal, walk away from it. You may pass up a good deal or two doing this, but as a rule it is better to do that a few times than to get burned once.