With apologies to those irked by the zombie threads.... 

Item location is, for the most part, listing / item specific, because some sellers have warehouses all over the country, some have local stock as well as drop ship etc etc etc, so a global "seller location" isn't the same as "item location", although, yes, the info can be pulled from other addresses, previous listings and so forth, if the info isn't changed or updated elsewhere... in saying that, eBay doesn't always get it right, and sometimes will display an incorrect suburb based on the postcode, since they don't seem to understand that several suburbs can share the same PC (also, check all of your addresses listed under your account. Your primary / registered address is one thing, but eBay allows you to input several other addresses, including a pick-up address, return address, separate postage address etc, and I'm pretty sure they will use the pick up or return address if the primary registered address is different - my item location is where my return address is located, which is a PO box in a different suburb to my residence).

Anyway....

Here's where to change the item location on an individual listing (located after all of the postage options):