Answer:
Most are not. A very few are. All of the seances and medium-invoked apparitions that were publicly reported during the Victorian and Edwardian eras were most likely faked performances created to separate a wealthy populace from their money. This trend has continued on into the modern era with phone psychics and television shows.
However, there are ways to establish legitimate contact beyond the veil. All of them have a degree of risk associated with their operation.