This was my thought too. I've already asked you to "fix it for me" once. I feel to do so again would just be rude (and wasteful as now 2 slices would have to be put aside for another person, or thrown out)

By extension, asking for a change in itself is presumptuous, so coming back with the same product is returning the favor.

Quite true. Or they may be hesitant to be push too much. Or they might just mentally note to not come this way again. All feedbacks need not be verbal.

Maybe for some, but even rude and abusive people do it.

I worked in a poor area. The people who live there, by and large, don't give a shit what you think of them.