How can one performing Istikhara be sure that their choice is based on divine guidance and not on personal whims, especially when they fear interpreting events as divine messages? And what is the way to ensure the correct choice in Istikhara?

A Muslim should supplicate with certainty of response, and ask Allah to facilitate the matter for him if it is good, or to divert it from him if it is evil. If he performs the Istikhara prayer, he should proceed with what he feels comfortable with and what his heart inclines to, as long as it is not due to personal whims. Dreams have no bearing on the matter, and there are no divine messages that come to the one who performs Istikhara. He should be content with what Allah has decreed for him after the Istikhara.