when you buy you buy it with the whole logbook you fill in the trade slip for them to send off, the yellow bit on the top right, what name you choose to put on the trade slip is up to you
they then send that off and it comes out of there name and shows on the dva pooter etc as in trade, worth also noting in trade cars dont need to be sorned either if no tax as there in trade hands
i declare many cars to the tax man but theres prob 20 odd a year i dont