More-or-less continuing from yesterday, there’s a whole other area of support for your claims you might call “evidence” rather than “proof.”
Probably most basic on that is FEATURES.
Your claims are going to be benefits. “Look younger in 30 days.”
If you then describe the features which lead to those benefits, that supports your claim and makes it more believable. “Only Shruk brand facial creme contains 30,000 I.U. of Vitamin E per ounce.”
Any relevant, specific facts you can marshal will support and build confidence in your benefits.
It also helps if your claims are as specific as possible. Not “almost double” but “89% improvement.”