How do you know your AI receptionist is actually following its instructions?

Picture a call to a wellness-clinic agent. The caller asks what a primary service costs. Nothing in the agent's system prompt mentions a price. The agent says "$179 to start."

The clinic doesn't charge $179 for that service.

One call. One sentence. A made-up number that the customer is now repeating to their spouse, their friends, and possibly an attorney if it ever shows up on an invoice.

That's the problem voice AI quietly creates. Large language models are probabilistic. The same prompt produces a slightly different call every time. Most of the variance is invisible — small wording differences nobody notices. Some of it is a price the agent invented, a guardrail it skipped, or a piece of legal advice it should never have given.

You usually find out from the customer. Or the lawyer. Or the one-star review.