Evidence that supports your claims.
WHY IT MATTERS
You saying you are good is a claim. A customer saying it is evidence.
For an unfamiliar business, this is frequently what decides whether someone contacts you.
WHAT WORKS
A real name, and ideally a photograph or a business name
Something specific: what the problem was, what you did, what the outcome was
Recent, or undated if timeless
"Excellent service, highly recommended" from "J.O." is worth almost nothing. "They rewired our office over a weekend so we lost no trading days" is worth a great deal.
HOW TO GET THEM
Ask, after the work, directly. Most satisfied customers oblige.
Ask a specific question: "what problem were we solving, and how did it go?" That produces something usable rather than generic praise.
OTHER PROOF
Photographs of actual work Client logos, with permission Credentials and certifications
Numbers: how many, how long, how much
WHERE TO PUT IT
Near the point of decision: on service pages, near the call to action, not only on a testimonials page nobody visits.
WHAT NOT TO DO
Invent them. Readers recognise fabricated testimonials.