the best approach to scoping is for the customer to state upfront what is needed, even before the requirements are collected.
of course, the customer must never stop user asking for what they want, even if some items are slightly out of scope. that does not mean that those requirements will never be implemented. keep them, but mark them as "to be implemented later" in other words, give them a priority. this is far better than deleting requirement, only to have them requirement introduced and requirement argued at the next review meeting.