Do you mean writing postage policy in the listing? I don't think you have to.I do just to make things easier,not that most buyers read such things anyway.

Or do mean postage policy in the settings? I have mine set to post only to Aus.

Also,look at the Buyer Requirements settings,under Seller Account,then Site Preferences.You can block buyers from certain countries,buyers with unpaid item strikes etc.

With item description,i add all measurements just to cover all bases on sizing.Again, most buyers don't read much of that & you aren't required to.