Answer by taking a quote from the following article:

Although Price claimed his birth was in Shropshire he was actually born in London in Red Lion Square on the site of the South Place Ethical Society's Conway Hall. He was educated in New Cross, first at Waller Road Infants School and then Haberdashers' Aske's Hatcham Boys School. At 15, Price founded the Carlton Dramatic Society and wrote plays, including a drama, about his early experience with a poltergeist which he said took place at a haunted manor house in Shropshire. According to Richard Morris, in his recent biography Harry Price:

On 4 February 1922, Price with James Seymour, Eric Dingwall and William Marriott had proven the spirit photographer William Hope was a fraud during tests at the British College of Psychic Science. Price wrote in his SPR report "William Hope has been found guilty of deliberately substituting his own plates for those of a sitter ... It implies that the medium brings to the sitting a duplicate slide and faked plates for fraudulent purposes."  Price secretly marked Hope's photographic plates, and provided him with a packet of additional plates that had been covertly etched with the brand image of the Imperial Dry Plate Co. Ltd. in the knowledge that the logo would be transferred to any images created with them. Unaware that Price had tampered with his supplies, Hope then attempted to produce a number of Spirit photographs. Although Hope produced several images of spirits, none of his materials contained the Imperial Dry Plate Co. Ltd logo, or the marks that Price had put on Hope's original equipment, showing that he had exchanged prepared materials containing fake spirit images for the provided materials.  Price later re-published the Society's experiment in a pamphlet of his own called Cold Light on Spiritualistic "Phenomena" - An Experiment with the Crewe Circle. Due to the exposure of Hope and other fraudulent spiritualists, Arthur Conan Doyle led a mass resignation of eighty-four members of the Society for Psychical Research, as they believed the Society was opposed to spiritualism. Doyle threatened to have Price evicted from his laboratory and claimed if he persisted to write "sewage" about spiritualists, he would meet the same fate as Houdini. Doyle and other spiritualists attacked Price and tried for years to have Price take his pamphlet out of circulation. Price wrote "Arthur Conan Doyle and his friends abused me for years for exposing Hope."

How was he a fraud?
William Hope has been found guilty of deliberately substituting his own plates for those of a sitter ...