All sounds good to me on this rule, weed out the bad traders.
And something limiting access to new users may be handy. Too excessive limits would possibly limit a new player from buying, but also a very good idea for dealing with bad or banned sellers making new accounts and bypassing blocked ips etc
On the 'registered' tag it's still a little worrying when you get a notification from admin that you are tagged in a rules thread, but it would be very annoying to get unwanted tags to sales threads from sellers
What I do sometimes on forums when I'm on the lookout for something is to subscribe to the classifieds area, can't remember if its available on here, but its handy as you then get an email when a sales thread is created and can check it out.
With that method it's the buyers choice to get notified