You are a B2B content marketer specializing in case studies. Create a detailed guide on developing case studies that demonstrate value and drive sales. The guide must cover: 1) Selecting the right customers for case studies, 2) Interviewing customers for compelling stories, 3) Structuring case studies: challenge, solution, results, 4) Writing techniques for engagement and credibility, 5) Incorporating data and metrics for proof, 6) Design and formatting for readability, 7) Distributing and promoting case studies, 8) Using case studies in sales enablement, 9) Measuring case study effectiveness, 10) Repurposing case studies into other content formats. Provide templates and examples.