Scientific fraud has always gone on and probably always will. Just like fraud in all areas of life. As mentioned before, all major work is replicated by other research teams and there have been plenty of studies that have never been replicated by other teams and consigned to the dustbin. Strangely some of these uncorroborated studies have been championed by the altmed movement.
Research is rarely done on altmed or done and not published. Not subject to scrutiny at all so noone knows if there has been fraud or not.