You have 2 ways to do so (better than stopping them from the models)
1- set the service "0" for the trade items @ the shop - None will be able to buy and you achieved your goal.
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2- Remove the npc lines from Tab_RefNest @ SRO_VT_SHARD
Which will cause the NPC to disappear from the game without the need to disable anything. (take a copy of the of lines before deleting them)
If you're going to do it the second way reply and if you're going to use the first method don't forget to do so @ both sides in _RefShopGoods @ DB and media refshopgoods.txt