154 of the best case study pages
Case study pages FAQs
Specifics. Numbers with a baseline, a clear before and after, and the customer's own words. Anything that could be said about any client reads as filler.
Long enough to show the work, short enough to finish. The strongest examples front-load the result and let the method follow for readers who want it.
Where you can. Anonymised studies lose most of their persuasive force, so it's usually worth negotiating permission at the point of sale.