Companies now prefer to deliver high value features. Company commits to deliver high quality product defined by the agreed upon Definition of Done. Customer participates actively with Scrum team, keep himself available and engaged during the entire project.
Customer shall be able to make changes to the Scope without incurring any additional cost if total Scope of contracted work is not changed. New features may be added for free at Sprint boundaries if items of equal scope are removed from the contract.
The customer is expected to be active in the project prioritizing features by business value and get it implemented in order to get maximum value, participate in each sprint planning by discussing selected features with team answering question to provide clarification. Participate in writing conditions of satisfaction for each feature so that the team has the clear definition of done. At sprint reavie provide feedback for both work-in-progress and completed work. He also participate responsibly in grooming the backlog where high value items are swapped with comparative low value items.
Book: The Art of Doing Twice the Work in Half the Time by Jeff Sutherland
Book: Succeeding with Agile, Software development using Scrum