Jinn Possession (or Masaha) is a kind of sickness. If a person who has this sickness is rational, then he has the choice and he will be brought to account for his words and actions. The fact that we cannot see the jinn does not mean they do not exist either. This is the view of the materialists of our age and those who followed in their footsteps. Indeed, how many are there things that our eyes cannot see but whose effects are noticeable? While the examples are many and varied, including air, electricity and limited to this etc. For details see: JINN POSSESSION 
Magic/ sihr is a serious crime. Sihr is so called because its means are hidden or secret, and because the practitioners of sihr deal with things in secret which enable them to perform illusions to confuse the people and deceive their eyes, and to cause them harm or steal their money, etc., in a secretive manner so that in most cases nobody realizes what is happening. For details see: Magic 
Many of us are unaware of the harms of Hasad (Envy) or El 'Ayn (the Evil Eye). The 'ulamaa' (scholars) of the El-Lajnah El-Daa'imah (Standing Committee for Islaamic Research) were asked to define al-ayn. They responded with the following: "The Arabic word El-'Ayn (the 'ayn) refers to when a person harms another with his eye. It starts when the person likes a thing, then his evil feelings affect it, by means of his repeated looking at the object of his jealousy. For more see: evil eye 
All the above (Jinn possession, sihr or Al ayn) are treated by Raaqi.
A Raaqi is a person who has studied and understands the science of Ruqya according to Quran and Sunnah and who treats people and assists them in the treatment against Sihr(magic), Shirk(polytheism) and Jinn. There are many different methods of Ruqya, but what makes a person a true Raaqi is one who practices Ruqya according to the Quran and Sunnah.
The method that is adopted is simple, easy to understand, easy to learn by even non-ulema and is totally free from all Shirk related things.
OR The term ‘Raaqi’ is used for an Islamic ‘Spiritual healer’ or exorcist and refers to someone who has knowledge of Islam, of Ruqyah treatment through education and experience, and performs ruqyah treatment for individuals with ailments who are unable to perform ruqyah upon themselves (self ruqyah). A person may not be able to perform Ruqyah on themselves if they are severely unwell or do not have sufficient knowledge or understanding of their ailment.
He will be somebody who firmly believes in Tawheed and is free from all types of shirk, kufr and misguidance and does not associate himself with beliefs/actions that may lead one to fall into any of these categories.
There is nothing wrong with the Muslim reciting ruqyah for himself. That is permissible; indeed it is a good Sunnah, for the Messenger (peace and blessings of Allaah be upon him) recited ruqyah for himself, and some of his companions recited ruqyah for themselves.
It was narrated that ‘Aa’ishah (may Allaah be pleased with her) said: When the Messenger of Allaah (ﷺ) was ill, he would recite al-Mi’wazatayn over himself and spit drily. When his pain grew intense, I recited over him and wiped him with his own hand, seeking its barakah (blessing).” Sahihal-Bukhari, 4728; SahihMuslim, 2192 For More: Dua and Azkar 
With regard to the du’aa’ that is prescribed for the Muslim to say if he wants to recite ruqyah for himself or for someone else, there are many such du’aa’s, the greatest of which are al-Faatihah and al-Mi’wadhatayn.
A group of the Companions of the Prophet (peace and blessings of Allaah be upon him) set out on a journey and travelled until they made came near one of the Arab tribes. They asked them for hospitality but they refused to do so. Then the leader of that tribe was stung, and they tried everything but nothing helped him. Then some of them said, Why don’t you go to those people who are staying (nearby)? Maybe some of them have something. So they went to them and said, O people, our leader has been stung and we have tried everything and nothing helped him. Do any of you have something? One of them said, Yes, by Allaah. I will perform ruqyah for him, but by Allaah we asked you for hospitality and you did not give us anything, so we will not perform ruqyah for you unless you give us something in return. So they agreed on a flock of sheep, then he started to blow on him and recite Al-hamduLillaahiRabbil-‘Aalameen. Then he recovered quickly from his complaint and started walking, and there was nothing wrong with him. Then they have them what they had agreed to, and some of them (the Sahaabah) said, Let us share it out. The one who had performed ruqyah said, Do not do anything until we come to the Prophet (ﷺ) and tell him what happened, and we will wait and see what he tells us to do. So they came to the Messenger of Allaah (peace and blessings of Allaah be upon him) and told him what had happened. He said, “How did you know that it is a ruqyah?” Then he said, “You did the right thing. Share them out, and give me a share.” And the Messenger of Allaah (ﷺ) smiled.Sahih al-Bukhari, 2276, and Sahih Muslim, 2201
It was narrated that ‘Aa’ishah (may Allaah be pleased with her) said: When the Messenger of Allaah (ﷺ) was ill, he would recite al-Mi’wazatayn over himself and spit drily. When his pain grew intense, I recited over him and wiped him with his own hand, seeking its barakah (blessing).” Sahihal-Bukhari, 4728; SahihMuslim, 2192
Ibn ‘Abbaas (may Allaah be pleased with him) said: The Prophet (ﷺ) used to seek refuge for al-Hasan and al-Husayn, and he would say: “Your father [ meaningIbraaheemm peace be upon him] used to seek refuge with Allaah for Ismaa’eel and Ishaaq with these words: 'U'eezubikalimaatil-laahit-taammati min kullishaytaaninwahaammatin, wa min kulli 'ayninlaammatin. (read this 1 time)(Meaning: I seek refuge in the perfect words of Allaah, from every devil and every poisonous reptile, and from every evil eye).’” Sahihal-Bukhari, 3191 
Allah knows best
Remember:They perform the Ruqya while Allah is the one who cures.