In the name of Allah, and all praise is due to Allah, and peace and blessings be upon the Messenger of Allah.
Indeed, as long as a person is alive, they are not safe from trials. We may think well of someone, only to find later that they have turned away, as you have seen with the example of Waseem Youssef. When we think well of someone, and they change, many people might associate our previous good opinion with their later actions. For instance, some people hold the scholars who previously praised Rabi’ al-Madkhali accountable for all the faults that emerged from him after their praise. Sometimes we might think well of a person, while there are things hidden from us during that time of good opinion, as happened to me when I thought well of some teachers until I learned of their clear violations in the fundamentals of the religion. These matters instill fear in anyone wanting to praise someone, and Allah’s help is sought. A person might even study under a Shaykh for a period before realizing his deviation, so how about when someone advises others about someone they’ve only known from afar without ever meeting them!
Ibn Taymiyyah said about the most famous heretics:
“I used to, in the past, think well of Ibn Arabi and hold him in high regard because of the benefits I found in his books, such as his words in many parts of the Futuhat… and the like. But at that time, we had not yet discovered his true intentions, nor had we studied Fusus and similar works.”
(Majmu’ al-Fatawa, 2/464)
And I advise with the Book (Qur’an) and the Sunnah, and then with the books of the Salaf (the righteous predecessors). Whoever, whether great or small, follows them and adopts them as their path, I recommend him. But whoever opposes them with his own opinions and desires, or gives precedence to the views of the theologians or the latecomers over them, I disavow any recommendation of him.
Just as the leader of the deviants and disputers disavowed his unitarian teacher, whom he used to visit two or four times a year and take his students to, and said: “(I repented to Allah from his companionship and from deliberately meeting him, and from anything that might have reached my ears from his words that I did not explicitly reject, which was contrary to the Shari’ah. I made repentance for that.)” (Al-Istiqadh wal-Tawbah).