What evidence makes you trust a business-critical API?

When an API affects payments, tax, accounting, identity, or other business-critical operations, a successful response is not enough for me to trust it in production.

I usually look for several things:

• clear provenance for the underlying data

• documented historical or versioned behaviour

• transparent failure states

• audit logs or traceable request records

• a realistic sandbox

• security and reliability documentation

• responsive support when something goes wrong

I’m curious how other founders and developers evaluate this.

What evidence do you need before integrating a business-critical API into production?

Have you ever rejected an otherwise promising API because an important trust signal was missing? What was it?