I like how the 5e DMG encourages the DM to establish "Table Rues" about things like how you (as DM) will be running dice rolling. It feels like as long as the DM has let them know it might happen it isn't "lying" to them in the moral sense -- since they've agreed to the rules.I really don't think that is what is intended.
For example, am I fudging rolls if I just decide that this particular action should be an automatic success in a certain context that comes up? And sometimes I'll make rolls behind the screen just to raise the narrative tension, especially if the players are taking too long. That's "lying" to them, but I don't think it's unethical.
I am always amazed at how players can view things I think have very similar effects very differently (can I fudge a monsters damage roll down vs. can I have it choose to attack very sub-optimally).
I've sometimes pondered the idea of having a DM equivalent of inspiration to avoid the urge to do it to often.