It is not permissible to inflict harm upon oneself. Since smoking has many harmful effects on one’s health, it is not permissible to smoke.
Allah swt says in the Quran what could be translated as:
“… He commands them to do good and forbids them from evil, permits for them what is lawful, and forbids to them what is impure/harmful… ” Al-A’raf – verse 157
It is not permissible to sell cigarettes too, as by selling cigarettes one will be guilty of assisting in committing a sinful act.
Allah swt says what could be translated as:
“… Cooperate with one another in goodness and righteousness, and do not cooperate in sin and transgression. And be mindful of Allah… ” Al Ma’dah – verse 2
It is not permissible for you to sell cigarettes whether you are the owner of the store or a worker because the Prophet (peace and blessings of Allaah be upon him):
“… when Allah forbids a thing He also forbids its price.” Narrated by Ahmad and Abu Dawood (3026)