What does « To buy / To sell » mean in the Quran?

And they followed [instead] what the devils had recited during the reign of Solomon. It was not Solomon who disbelieved, but the devils disbelieved, teaching people magic and that which was revealed to the two angels at Babylon, Harut and Marut. But the two angels do not teach anyone unless they say, "We are a trial, so do not disbelieve [by practicing magic]." And [yet] they learn from them that by which they cause separation between a man and his wife. But they do not harm anyone through it except by permission of Allah. And the people learn what harms them and does not benefit them. But the Children of Israel certainly knew that whoever purchased the magic would not have in the Hereafter any share. And wretched is that for which they sold themselves, if they only knew.

Indeed, they who conceal what Allah has sent down of the Book and exchange it for a small price - those consume not into their bellies except the Fire. And Allah will not speak to them on the Day of Resurrection, nor will He purify them. And they will have a painful punishment.

Those are the ones who have exchanged guidance for error and forgiveness for punishment. How patient they are in pursuit of the Fire!

And of the people is he who sells himself, seeking means to the approval of Allah. And Allah is kind to [His] servants.

Indeed, those who exchange the covenant of Allah and their [own] oaths for a small price will have no share in the Hereafter, and Allah will not speak to them or look at them on the Day of Resurrection, nor will He purify them; and they will have a painful punishment.

Indeed, those who purchase disbelief [in exchange] for faith - never will they harm Allah at all, and for them is a painful punishment.

And [mention, O Muhammad], when Allah took a covenant from those who were given the Scripture, [saying], "You must make it clear to the people and not conceal it." But they threw it away behind their backs and exchanged it for a small price. And wretched is that which they purchased.

And indeed, among the People of the Scripture are those who believe in Allah and what was revealed to you and what was revealed to them, [being] humbly submissive to Allah. They do not exchange the verses of Allah for a small price. Those will have their reward with their Lord. Indeed, Allah is swift in account.

Have you not seen those who were given a portion of the Scripture, purchasing error [in exchange for it] and wishing you would lose the way?

So let those fight in the cause of Allah who sell the life of this world for the Hereafter. And he who fights in the cause of Allah and is killed or achieves victory - We will bestow upon him a great reward.

Indeed, We sent down the Torah, in which was guidance and light. The prophets who submitted [to Allah] judged by it for the Jews, as did the rabbis and scholars by that with which they were entrusted of the Scripture of Allah, and they were witnesses thereto. So do not fear the people but fear Me, and do not exchange My verses for a small price. And whoever does not judge by what Allah has revealed - then it is those who are the disbelievers.

O you who have believed, testimony [should be taken] among you when death approaches one of you at the time of bequest - [that of] two just men from among you or two others from outside if you are traveling through the land and the disaster of death should strike you. Detain them after the prayer and let them both swear by Allah if you doubt [their testimony, saying], "We will not exchange our oath for a price, even if he should be a near relative, and we will not withhold the testimony of Allah. Indeed, we would then be of the sinful."

They have exchanged the signs of Allah for a small price and averted [people] from His way. Indeed, it was evil that they were doing.

Indeed, Allah has purchased from the believers their lives and their properties [in exchange] for that they will have Paradise. They fight in the cause of Allah, so they kill and are killed. [It is] a true promise [binding] upon Him in the Torah and the Gospel and the Qur'an. And who is truer to his covenant than Allah? So rejoice in your transaction which you have contracted. And it is that which is the great attainment.

And they sold him for a reduced price - a few dirhams - and they were, concerning him, of those content with little.

And the one from Egypt who bought him said to his wife, "Make his residence comfortable. Perhaps he will benefit us, or we will adopt him as a son." And thus, We established Joseph in the land that We might teach him the interpretation of events. And Allah is predominant over His affair, but most of the people do not know.

And do not exchange the covenant of Allah for a small price. Indeed, what is with Allah is best for you, if only you could know.

And of the people is he who buys the amusement of speech to mislead [others] from the way of Allah without knowledge and who takes it in ridicule. Those will have a humiliating punishment.