Can anyone see a devil? Is it possible? If someone saw a devil then what are the consequences? And what are the reasons that why that specific person saw a devil?
First of all, it depends on what do you mean by "seeing". Seeing his true form? Or any form?
According to this fatwa, it is possible somehow. There are 3 mentioned cases:
1) The jinn may appear in the form of a human being as recorded in Sahih al-Bukhari when a devil came to Abu Hurairah (Radiya Allahu Anhu) in the shape of a poor man and Abu Hurairah found the devil taking much food of charity.
2) The jinn may appear in a form of black dog as confirmed in Sahih Muslim that the Prophet (Sallallahu Alaihi wa Sallam) said: "A black dog is devil". Ibn Taimiya (May Allah's Mercy be upon him) said: 'The black dog is a devil, and the jinn often appear in its form, since the black color can bring the devilish powers more than other colors.
3) The jinn can appear in the shape of snakes. Thus, the Messenger (Sallallahu Alaihi wa Sallam) banned killing home snakes lest may any of them be a Muslim jinn. Abu Said al-Khudri (Radiya Allahu Anhu) said that Allah's Messenger (Sallallahu Alaihi wa Sallam) said: "There are Muslim Jinn in al-Madina: If one appears to you, in any form, you are to admonish it to depart for three days. If it appears after that, you must kill it, for it is truly a devil". [Reported by Imam Muslim]