Mistakes made when cutting the hair or shaving the head
Question

What are the mistakes that some people make when shaving their heads or cutting their hair?.
Praise be to Allah.Among the mistakes that are made when cutting the hair or shaving the head are the following: 
-1-  
Some people shave part of the head completely with a razor, and leave the rest. I have seen that with my own eyes. I saw a man doing saa’i between al-Safa and al-Marwah, and he had shaved half of his head completely and left the rest of his hair. I grabbed him and said to him, “Why did you do that?” He said, “I did it because I want to do ‘Umrah twice, so I shaved half for the first ‘Umrah and left half for this ‘Umrah.” This is ignorance and misguidance that none of the scholars ever suggested. 
-2- 
Some people, when they want to exit ihram of ‘Umrah, cut a few hairs on their head, on one side only. This is contrary to the apparent meaning of the verse in which Allah says (interpretation of the meaning): 
 
“…(some) having your heads shaved, and (some) having your head hair cut short…” [al-Fath 48:27]
The shortening of the hair should have an obvious effect on the head. It is known that cutting one or two or three hairs does not have any effect and it is not apparent that the pilgrim who has done ‘Umrah has in fact shortened his hair. So he is going against the apparent meaning of the verse. 
The remedy for these two mistakes is for the one who wants to shave his head to shave all of it, and to shorten the hair all over the head if he wants to cut it, and not to cut just one or two hairs. 
-3- 
There are some people who, when they have finished saa’i, if they cannot find anyone to shave their heads or cut their hair, they go back to their houses and exit ihram, and put on regular clothes, then they shave their heads or cut their hair after that. This is a serious mistake, because a person cannot exit ihram without shaving his head or cutting his hair, as the Prophet (peace and blessings of Allah be upon him) said, when during the Farewell Pilgrimage he commanded those of his companions who had not brought a hadiy (sacrificial animal) to make it ‘Umrah, and he said, “Let him cut his hair then exit ihram.” Narrated by al-Bukhaari, 1691; Muslim, 1229.  This indicates that one cannot exit ihram until after cutting the hair. 
Based on this, if a pilgrim finishes saa’i and cannot find someone to cut his hair, he should remain in ihram until he shaves his head or cuts his hair; it is not permissible for him to exit ihram before that. If we assume that a person did that out of ignorance and exited ihram before shaving or cutting his hair, thinking that it was permissible to do so, there is no blame on him because of his ignorance, but when he finds out about that he should take off his regular clothes and put on his ihram garments, because it is not permissible to continue exiting ihram when he knows that it is not permissible. Then when he has shaved his head or cut his hair, he may exit ihram.”