The eighth criterion is that he must claim to be from Allah. It is not for others to say he is a Prophet, he must claim it, otherwise the 1st criteria will not come into place. Allah will not seize someone by their life-artery if they themselves have not made any such claim. The blame will revert to the person who has made such a boast on his behalf.
The Holy Qur'an states
Allah chooses His Messengers from among angels, and from among men
The Holy Bible states
Jesus said "For I proceed forth and came from God; neither came I of myself but He sent me"
Holy Bible, John Chapter 8, verse 42
It is therefore vital that the person should claim to be a Prophet, after of course, being informed by God that he is. It is only after Allah has informed them, that they can make such a claim. We see that John the Baptist, may peace be upon him, was asked whether he was Elijah and he denied it. (John 1:21) But later on, Jesus, may peace be upon him, said that John the Baptist is Elijah, believe it or not. (Matt 17:10-13)
From this we understand that Allah didn’t inform John the Baptist in the beginning that he was the spiritual coming of Elijah and that is why he could not make the claim, but then Allah informed Jesus that John was indeed the second coming of Elijah, and that is why Jesus went to John and the sign of the dove came, as John was meant to forewarn the coming of the Messiah. So unless Allah has informed them, they can't make any claim.
Concerning Hadhrat Mirza Ghulam Ahmad, may peace be upon him, he kept receiving dreams and revelations saying that he was representing the second coming of Jesus. He thought like all the Muslims at that time, that Jesus was alive in Heaven. Finally, he decided to investigate and see what the Holy Qur'an states and was surprised to find over 30 references showing that Jesus could not be alive in Heaven. He then turned to the Holy Bible and again found 30 references proving that Jesus did not die. Now he understood why Allah kept calling him Jesus and later on wrote the book 'Jesus in India'. http://www.alislam.org/library/books/Jesus-in-India.pdf. So only after Allah made it clear to the Promised Messiah that he was a Prophet, did he make the claim.