Quality is delighting customers
If requirements are changing continuously , one should initiate the following steps
1) Let the higher authority or manger know , what are the problems we are facing due to continuous requirement changing? How the deadline of delivery would affect due to this..? Because of requirements changes developer & QA team have to rework from beginning.
2)Force the higher management to let client know how our team are suffering & by what depth we are suffering . If client understand our suffering & decide not to change requirement further then it is ok . But if Client do not listen us & continuously ask requirement changes Then we should charge them accordingly .
In my view , it is sufficient