How do you handle a client who keeps changing the project scope?

[Btaliat]

Freelancers should make sure that you are making your clients respect your contract. There are some clients that always want to take advantage of the clients. Freelancers must make sure that they refer their clients to the contract, and if such quote is not in the contract, you can add it. Tell them that you need to be adding extra cost for extra and additional task. If you don't do this, you may not finish the task on time and you may not get value of your money. What do you think about this?