Your restaurant makes the best omelet in town? Says who?

When you praise yourself, it's not very believable. When a neutral third-party says something good about you, you can use that as a reference and instantly make your claim much more believable.

This is why you need to use

* customer testimonials (full name + photo or video),
* neutral expert opinions,
* third-party reviews,
* verified (scientific) studies

to back up any claim you make.