Most collections of testimonial examples are a list of nice sentences with nothing to learn from. The useful version explains what each one does: names the problem, carries a number, comes from somebody the reader recognises as themselves. This page is the shapes worth aiming at and the ask that produces each, because the example you admire is the answer to a question somebody asked well.
The before-and-after
'We were quoting by hand and it took two days; now it takes an hour.' It works because it is specific and falsifiable, and it comes from asking what the situation was before rather than what they think of you.
The number
'It paid for itself in the first month.' The most valuable and the hardest to get, because it needs a customer who measured. Ask the ones who did. A customer who tracked the before and after will usually give you the figure if you ask for it directly, and will almost never volunteer it if you do not.
The objection answered
'I thought we were too small for this.' This one earns its place next to the price, because it says out loud what the reader is thinking. It comes from asking what nearly stopped them buying. It is also the shape most businesses have and never publish, because the customer said it in passing on a call rather than in writing.
Questions people ask about customer testimonial examples
Can I use somebody else's testimonial as a template?
As a shape, yes. Never as words: a testimonial has to be what the customer actually said.
Should I show the customer examples when I ask?
One, and short. It tells them the size and register you mean, without steering the content.
What if all my testimonials are vague?
Change the questions rather than the customers. Vague answers are nearly always the fault of the ask.