Customers lose faith if you are months into a project and need to redesign some work item every week. Attempt to get all design details done and communicate about those design decisions up front. As a provider, walk through the whole execution conceptually and figure out all the questions that need answering first.
Engage the customer in a high-level walkthrough of the project and derive answer to those questions. During the design stage, gather information and understanding from sessions with the customer but organize the designs into work plans away from them to save time (yours and theirs).