Returning used items from Amazon

I'm trying to only return used items with the Amazon Product Advertising API

public function itemLookup($items, $responseGroup = 'Offers,Images,BrowseNodes,ItemAttributes,OfferFull')

and then I set the condition to used:

"Condition"=>"Used",

and return:

echo "Used: " . $items->OfferSummary->TotalUsed;

But this returns all new and used items. Any idea why?