The best category for an item I want to list is one that only has Simple Delivery, which would cost £2.72.  In a different category, which is OK but not quite as good, I can post it with Custom delivery for 91p.  

So it's a dilemma as to whether it will stand more chance of selling in the best category at a higher price to take account of the high postage cost, or in a less good category at a lower price due to the cheaper postage cost.

Heaven forfend that ebay could give everything the best chance of selling by making all categories available with Custom postage if the item is under £20 ☹️