I agree with the other posters here that, without seeing images or knowing more details, it sounds like user error. When I used to sell cameras, I used to have customers come in all the time with concerns that sound much like yours, and in all but one case where the camera was actually defective, the image problems resulted from a user who relied on the camera to know more about photography then he/she wanted to learn.
I don't want to sound harsh, believe me, but this sounds to me much like, "I have friends who can paint beautiful paintings. I bought the same type of paint and brushes and the same brand of canvas, but my paintings don't look as good. Is there something wrong with the brush?"
Instruction manuals tell what your camera's different knobs, buttons and switches do, but they don't give any foundation in photography. However, there are numerous books at your local bookstore or library that should go way beyond the instruction manual and help give a good foundation in photography. (Usually when I suggested this at the camera store my customers told me they didn't want to get THAT into photography. They REALLY wanted the camera to do the work.)
Anyway, the best camera in the world can only do so much, the rest will be up to you. You'll have to decide if better photos are worth the investment in time and knowledge.
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A camera is just a tool - no matter how much one loves it.