How do you know if a medium is fake?

How do you know if a psychic is faking their mediumship? I recently saw my very vulnerable, grieving friend go through something with a psychic that set off my alarm bells. I believe in psychic ability, but I don't think everyone that claims that ability is honest.

My friend's parent died a couple of weeks ago. They went to a well-regarded psychic for guidance and for help communicating with their parent. The psychic did not know their dad had died. They said it was too early to communicate and they couldn't get much information and then gave a bunch of vague advice and insight that would apply to anyone while my friend sat there gently crying.

I'm not psychic but when my close relatives die, I feel like the strongest messages come shortly after death. There is no period of time that they waited to communicate, but rather, communication faded with time. Is there really some unspoken rule about when you can communicate with your dead loved-ones?

As I was sitting there listening to this psychic I couldn't get the thought out of my head that my friend's dead parent would hate this, would never want to communicate through this stranger, that they definitely would not want the psychic to make my friend cry, and that they would want their feelings to remain private feelings and not shared by a stranger.

I encouraged my friend to talk to their dead parent without a psychic helper. That they would hear and communicate back clearly and if not, it will still be cathartic.