Tell your customers the value they will get in exchange for the supply of their data. If the value isn't enough for them, let them withhold its collection.
Stewardship is as important as Custodianship. Increased business value and reduced life-time risk is driven by informed and disciplined use of data across the entire business.
Trust is built by respecting the limitations on purpose and retention. As the relationship progresses, let the customer maintain complete understanding and control of their data.