I plan to auction a vinyl record which could fetch quite a bit over £750.  I plan to do the thing where you say in the description that it's free postage and when creating the listing choose Simple Delivery and 'seller pays', then print the label to get the buyer's address and then separately arrange Special Delivery myself with RM.  If that's all correct my only question is how does ebay's system find out that the item was delivered?

Thanks in advance.