Making SD optional is the key policy change. For many it is fine, but it
has so many flaws it cannot be used to provide a quality buyer
experience, ad EBAY no longer seems to value giving good customer
service to buyers.

Key deficiencies are (IMO)

No ability to combine lots - the most serious failing of SD

No means to switch to COLLECT or DELIVERY. I do this a lot as we are
disposing of a lifetime's book collection with many local books, so I
deliver to local buyers for free and refund the postage.

No expedited shipping, Tracked 24 is not an expedited service, Special
Delivery is.

No access to cost effective large parcel services

I use Seller pays as it gives more flexibility as I get the label refund
and can then buy the correct delivery service, usually with Packlink.

A number of categories allow you to specify Custom Postage for items
stated to be Large Letters at the time of listing. If you made an error
and it will not fit a Large Letter it doesn't matter as you can select
the correct label for the packed parcel once sold via Packlink.