As long as your main concern is that the players are trying to gain some advantage, like having NPCs who help them, you just need to tell them. What worked for a DM in a previous game might very well not work for you.

I had players who reacted by swearing that this was not the case. Let's remove the temptation, I said. Then I proceeded to explain the division of power between players and DM in D&D and how thei rcontrol over NPCs could clash with the truths of the setting. This usually worked quite well.

Of course it would have been optimal to do that before the first session. Next time, maybe.

As long as your main concern is that the players are trying to gain some advantage, like having NPCs who help them, you just need to tell them. What worked for a DM in a previous game might very well not work for you.

I had players who reacted by swearing that this was not the case. Let's remove the temptation, I said. Then I proceeded to explain the division of power between players and DM in D&D and how their control over NPCs could clash with the truths of the setting. This usually worked quite well.

Of course it would have been optimal to do that before the first session. Next time, maybe.