Hi Tressygirl and thanks for  taking time to reply 

I would respectfully point out that I have no intention of  registering as a business seller, either now or in the future. Registering as a business seller places additional legal, administrative, and financial obligations on me which would not be appropriate to my circumstances as a private individual disposing of personal property

As I'm sure you're already aware from other user comments, I'm finding recent changes to eBay’s private selling structure is making casual private selling considerably more complicated and less attractive - including the introduction of Buyer Protection fees, delays in seller payments until delivery confirmation, increased pressure to use eBay-managed postage systems, along with a general move towards a business-style selling environment even for private individuals simply disposing of personal possessions.

As a retired individual selling surplus service spares (and other items) accumulated over many years, I don't consider it reasonable or appropriate to be treated as a commercial business operation. My activity is purely the disposal of long-held personal items rather than ongoing trade!

My original question still stands - how do I select appropriate postage AFTER a buyer has purchased if I offer free delivery? 

Thanks again 🙂