Away with the word customer case studies! It sounds too clinical and detached. Call it a ‘success story’, instead. Your client had a need or problem that no one could solve. You, or your organization, swooped in and provided a product or service that helped that person. Your client’s business soared, or his skin healed, or his dog recovered - whatever the case - you helped him live ‘happily ever after’.
That’s the crux of a ‘customer success story’.