Try this:
UPDATE `creature_template` SET `vendor_id` = '0' WHERE `vendor_id` = '1';
INSERT INTO `npc_vendor` (`entry`, `item`, `maxcount`, `incrtime`, `ExtendedCost`) VALUES
(5815, 16302, 0, 0, 0),
(5815, 16316, 0, 0, 0),
(5815, 16317, 0, 0, 0),
(5815, 16318, 0, 0, 0),
(5815, 16319, 0, 0, 0),
(5815, 16320, 0, 0, 0),
(5815, 16321, 0, 0, 0),
(5815, 16322, 0, 0, 0),
(5815, 16323, 0, 0, 0),
(5815, 16324, 0, 0, 0),
(5815, 16325, 0, 0, 0),
(5815, 16326, 0, 0, 0),
(5815, 16327, 0, 0, 0),
(5815, 16328, 0, 0, 0),
(5815, 16329, 0, 0, 0),
(5815, 16330, 0, 0, 0),
(5815, 16331, 0, 0, 0),
(5815, 16346, 0, 0, 0),
(5815, 16347, 0, 0, 0),
(5815, 16348, 0, 0, 0),
(5815, 16349, 0, 0, 0),
(5815, 16350, 0, 0, 0),
(5815, 16351, 0, 0, 0),
(5815, 16352, 0, 0, 0),
(5815, 16353, 0, 0, 0),
(5815, 16354, 0, 0, 0),
(5815, 16355, 0, 0, 0),
(5815, 16356, 0, 0, 0),
(5815, 16357, 0, 0, 0),
(5815, 16358, 0, 0, 0),
(5815, 16359, 0, 0, 0),
(5815, 16360, 0, 0, 0),
(5815, 16361, 0, 0, 0),
(5815, 16362, 0, 0, 0),
(5815, 16363, 0, 0, 0),
(5815, 16364, 0, 0, 0),
(5815, 16365, 0, 0, 0),
(5815, 16366, 0, 0, 0),
(5815, 16368, 0, 0, 0),
(5815, 16371, 0, 0, 0),
(5815, 16372, 0, 0, 0),
(5815, 16373, 0, 0, 0),
(5815, 16374, 0, 0, 0),
(5815, 16375, 0, 0, 0),
(5815, 16376, 0, 0, 0),
(5815, 16377, 0, 0, 0),
(5815, 16378, 0, 0, 0),
(5815, 16379, 0, 0, 0),
(5815, 16380, 0, 0, 0),
(5815, 16381, 0, 0, 0),
(5815, 16382, 0, 0, 0),
(5815, 16383, 0, 0, 0),
(5815, 16384, 0, 0, 0),
(5815, 16385, 0, 0, 0),
(5815, 16386, 0, 0, 0),
(5815, 16387, 0, 0, 0),
(5815, 16388, 0, 0, 0),
(5815, 16389, 0, 0, 0),
(5815, 16390, 0, 0, 0),
(5815, 22179, 0, 0, 0),
(5815, 22180, 0, 0, 0),
(5815, 22181, 0, 0, 0),
(5815, 22182, 0, 0, 0),
(5815, 22184, 0, 0, 0),
(5815, 22185, 0, 0, 0),
(5815, 22186, 0, 0, 0),
(5815, 22187, 0, 0, 0),
(5815, 22188, 0, 0, 0),
(5815, 22189, 0, 0, 0),
(5815, 22190, 0, 0, 0),
(5815, 23711, 0, 0, 0),
(5815, 23730, 0, 0, 0),
(5815, 23731, 0, 0, 0),
(5815, 23734, 0, 0, 0),
(5815, 23745, 0, 0, 0),
(5815, 23755, 0, 0, 0),
(5815, 25469, 0, 0, 0),
(5815, 25900, 0, 0, 0),
(5815, 28068, 0, 0, 0),
(5815, 28071, 0, 0, 0),
(5815, 28072, 0, 0, 0),
(5815, 28073, 0, 0, 0);
Insert into npc_vendor with this entry: (All demon trainers)
5815 / 5520 / 5753 / 6382 / 12807 / 16267 / 16649 / 23535