I do think they work differently for different people, however I have found that even if someone works pretty well for me, whatever other people complain about is likely to be a problem at some point. I have seen bad feedback and thought oh that doesn't sound right, the psychic is not like that, but eventually I'd see it too. It just depends whether it's something you can live with or not. Like I can accept if they get predictions wrong sometimes, I think that's inevitable, but I know other people will just cross them off their list and move on. Some people just want accuracy, and will put up with a reader who has an unpleasant personality, however I can't tolerate it if they are really pushy or blunt to the point of being unkind.
In some ways it's just like any other kind of business. When I drove foreign cars, I had to find mechanics who were good at working on those. However even if a mechanic was very knowledgeable about my type of vehicle, I would not want to deal with them if I felt they might try to scam me or overcharge me for their work. A hair stylist could be great for other people who have a certain type of hair, and horrible for you if your hair is different from what they usually work with. A massage therapist's technique could be too rough for someone else, but great for you. A restaurant might have a great reputation but when you try it, it's just not to your personal taste.
What makes this different though is it takes time to really find out how good a psychic is. I think some of them can see outcomes accurately, but they see it as immediate, when in reality like you said it might take years before it will happen.