When you promise a consequence, follow through. Try not to be influenced by your child's persuasive tactics. Children consistently test authority. Be prepared to follow through each time. Results, while not always immediate, will be forthcoming.
Children are just that - children.
Although they are learning to accept some responsibility, they are not yet adults, and should not be treated as such. Children need to know that their poor choices create consequences. Rewards and Consequences. Worthwhile rewards may help reinforce responsible actions. However, rewards do not have to be in the form of costly material gifts.