How can the suitor's qualities be examined to ensure his sincerity and prevent him from changing for the worse in the future?

The daughter is a trust with her father, and therefore he must choose a husband for her well, and he should be someone whose religiosity and character you approve of, according to the Prophet's (peace and blessings be upon him) saying: "If someone whose religiosity and character you approve of proposes to you, then marry [your daughter] to him. If you do not do so, there will be tribulation on earth and widespread corruption." And Al-Ghazali said: "Whoever marries his daughter to an oppressor, or a dissolute person, or an innovator, or a wine-drinker, has committed a crime against her religiosity and exposed himself to Allah's wrath."

Among the most important aids in choosing a righteous husband are: 1. Supplication (Du'a): It is the best means by which what is desired is achieved. 2. Asking trustworthy people: About the suitor and those closest to him, to know his comings and goings. 3. Seeking guidance (Istikhara): If trustworthy people praise the suitor, then seek guidance from Allah Almighty. 4. Advice and care after marriage: Parents should attend to their daughter and her husband with advice and care, check on their conditions, and give their daughter more advice to be a righteous wife who helps her husband.