READ TIME: Less than 30 seconds
Mark Shipped After AO is Complete prevents buyers from cancelling orders right after they buy from you. Some buyers try this as a tactic to get free products because they identify you as a drop shipper. They hope you'll refund them and forget to cancel the order at the source, but this prevents them from backing out of the sale.
eBay automatically removes the cancel option for the buyer with this enabled. 👍
Instantly mark all sales as shipped for your buyer is an extra option once "Mark shipped after AO is completed" is selected. The difference is the first one shows shipped after we finish AO usually in about 60 seconds; the other immediately shows shipped when your buyer checks out on eBay.