With every claim you make in your copy, you need to back it up. “We're #1,” “rated top in the industry,” or “highest quality” appear spurious if left as is.
By whose standards? In which publication? For which market?
Justify the claim to give it meaning.
But even justified claims are not enough. You need to link them to the reader somehow or else your claim, no matter how much you explain it, will seem self-serving and arrogant.
So turn the claim into a benefit.
“We are the highest quality because we use lab-tested materials and skilled workmanship that help prevent your widget from breaking down when you need it the most! That's why we offer the longest warranty in the business.”
If you need to credentialize a product, service, author, provider, or retailer, turn each credential into a meaningful, concrete benefit to the reader.