Yup! Sometimes, I actually offer them a discount in their “next order”. As I write this - issued someone an offer with $25 discount, simply because her previous order for troubleshooting turned to be one-minute tweak instead of programming gig.
That might sound a bit extreme and puritan. But I think fairness should go both ways. I have always been “don’t take an inch, don’t give an inch”. All my clients know what would happen when they ask for some little extra free work.