I find that people use the word 'topping', not knowing how to better phrase it. Generally what they mean is they want the crown reduced. Think about it, topping <u>is</u> a reduction of the crown, while not being a 'crown reduction'. They just may not know how to term it properly.
We (arborists) take topping to mean what it is, because we know the difference. The homeowner just wants to feel safe because their crown is really big, too much for their comfort.
The important thing after they say "I want my tree topped" is to ask them, "So what are your goals, what's your vision?" Nobody is going to answer, "I'd like a hat rack looking thing, ugly as sin with big, lopping cuts that will take a long time to recover, promise decay and offer me weakly attached regrowth."
Don't take to mean that exactly what they say ('topping') is really what they want. Ask more questions about the result they wish to see when you've completed the work. This really saves the time preaching against the ills of topping. I simply assume when someone says 'topping' that this is not actually what they want, but get clear with them on the goal because a proper crown reduction is far more involved than a topping.