sure as buttons

When you are absolutely sure of something but must exclaim that its diffidently true and accurate.

A button is always sure of itself. It's either pressed or not, buttoned up or not, clasped or unclasped.

CFO: Are you sure that the competitive analysis shows that we are outperforming our competitor?
Finance manager: Sure as buttons. The reports are as accurate as can be.

got had

When an individual gets tricked, mislead, lied or is confused about a given subject and then assumes they are right about said subject.

Individuals who usually fall for outlandish conspiracy theories or hold fanatical beliefs about a subject as a form of truth.

Joey: Vaccines are being used to kill people! There is no proof that they are helping us. It says it in the Bible.
Tom: Don't listen to Joey. He got had.