Nah its easier than that and you can even delete the npc.
just use:
Code:
DELETE FROM [Arcadia].[dbo].[NPCResource]
WHERE contact_script = 'NPC_Merchant_Creature_card_contact()'
If you want to keep that merchant and use it for another shop, the fastest would be to go into your resource/script folder. Open "NPC Merchant_Etc (e711e712dccb2680b678e4496717677d) .lua" and search for
Code:
dlg_menu( "@90996975", "open_market( 'Creature_card' )" )
and delete the line. Now that NPC cannot open the shop anymore.