There is no buyer / item received option for the buyer to mark, all they can do is to leave feedback.
Currently if you pack individually purchased items together , you'll have one tracking number and only payout for one will be released sooner, when tracking shows delivery , the payout for the other items will be held for a minimum of 14 days before release.
Combining postage under Simple Delivery is still not possible, eBay saying it's a technical issue and this happens on all devices not just the app.
Some sellers are leaving a message on their listing, for example..... ' If you wish to buy multiple items, please let me know before buying, I will relist them as one listing so only one postage cost is charged, combining postage is not currently possible. '
@jadutc-55