I only know you must not curse or hex the undeserving, and I do not believe in karma. I think it all depends on what you are taught and how you feel about it.
If you have a feeling it may backfire, dont do it, the feeling is your answer.
If you know it will bring something back to you, you can call it first before you do it, give the curse a consequence you are willing to take on, like, you know if he loses his hair, you might lose some of yours but that’s okay, you’re willing to take it (silly example, but you know).
But I still think with curses and hex, it always feels right with me because the person has done wrong, no doubt about it and they will pay and that is that.
I have had tiny incidents, when I was younger, but I cursed with fear and then felt guilt, even when the person was very bad…dont do that, dont have fear and guilt and still go ahead.
I protect myself, especially if I curse on behalf of someone, with prayer, salt, days of meditation before, white candle prayers with my saints and wear st Michael around my neck. And I always ask the spirits to decide whether this magick gets delivered or not ( because you never know if the person you’re helping is being 100% honest about the situation).
Also know your weak spot. I protect my psyche first because I use it the most and it’s open the most. I’m not afraid as much of physical backfire but I focus on psychic protection.
Its personal with curses. Depends a lot on you, your feeling, your strengths.