Well, this thread has been helpful for me.
I too thought that lifetime meant free. I have been wondering about upgrading to seller for a while, the main thing putting me off is that there is no indication of whether any buyers are interested or not so would it be worth £50 to find out? However, thanks to this thread, I can see that Platinum will probably be the best option for me if and when I finally make my mind up to upgrade!
Thanks Wizeguy