I've learned to do this with clients too. Some of them would call or email me with some really important, not previously discussed thing that they absolutely n

I've learned to do this with clients too. Some of them would call or email me with some really important, not previously discussed thing that they absolutely needed to have (but really didn't). Where in the past I'd immediately take this request seriously and discuss how many hours/days of work this would reasonably take, I now often give them an unusually high indication at first. If the conversation continues and it becomes clear that they really do want/need said feature, I'll come up with a more realistic indication.