Reviews
A roof replacement is one of the larger purchases a homeowner makes, and larger purchases get researched more carefully. Reviews carry outsized weight in that research.
The final walkthrough, when the customer can see the finished roof, is the strongest moment to ask, not a follow up call a week later once the excitement has faded.
A review with a photo of the finished roof adds real credibility that text alone doesn't. It's worth explicitly asking satisfied customers to include one if they're willing.