def similar(*asins)
      params = asins.last.is_a?(Hash) ? asins.pop : {:SimilarityType => :Random, :ResponseGroup => :Medium}
      response = call(params.merge(:Operation => :SimilarityLookup, :ItemId => asins.join(',')))
      arrayfy(response['SimilarityLookupResponse']['Items']['Item']).map {|item| handle_type(item, :item)}