public static function getUrl(array $prices)
 {
     global $tag, $marketplaceSingleCart;
     if (!$marketplaceSingleCart && count($prices) == 1) {
         return "http://www.amazon.com/gp/offer-listing/" . Isbn::to10(current($prices)->bookId) . "/condition=all&tag={$tag}";
     } else {
         return Amazon::getUrl($prices);
     }
 }