Back in the day sellers used to whack on massive postage and sell the item cheaply to pay less charges but then eBay cottoned on to that practice and charged a fee for both item plus postage, now a private seller doesn’t pay any charges, can’t see that lasting for long.
The change for the private seller going forward is that they only receive payment after the buyer has confirmed receipt or tracking confirmed delivery, obviously tracked postage is expensive. As Paul says you need to factor in all costs but that goes for anything you buy whether online or a physical purchase.
Tony