Honest weight, written terms, and what you could get away with
The Qur'an treats earning a living as ordinary and good. Once the Friday prayer ends, the instruction is to go back out and "disperse through the land and seek God's bounty". Work is where most people spend most of their waking hours, and the book meets them there rather than asking them to step away from it.
What follows the permission is a set of terms. Wealth may move between people "only through trade by mutual consent", and consent is what separates a sale from a taking. The line that has shaped Muslim commercial thinking for fourteen centuries sits in Surah al-Baqarah: "God has permitted trade and forbidden usury." Profit that comes from sharing a risk is allowed. A guaranteed return on another person's need is a different arrangement, and the verse names it.
Most of the commercial material is about weight. "Give full measure when you measure, and weigh with an upright scale" is addressed to whoever has a hand on the balance, and Shu'ayb says almost the same words to Madyan. The instruction assumes the scale can be tilted and that nobody would catch it, which is why it needs saying at all.
Surah al-Mutaffifin names something smaller and more common than large fraud. Its subject is the person who, "when they take a measure from others, demand it in full", and then gives less going the other way. The amount is small by design; anyone could absorb it and nobody would raise it. That is what earns it a surah.
The longest verse in the Qur'an is about paperwork. It covers a loan with a fixed term, says "write it down", and then works through the scribe, the witnesses, the borrower whose judgment is weak, and the exemption for a cash sale settled on the spot. Its stated reason is practical: a written record is "more equitable in God's sight, more sound as testimony, and more likely to keep you free of doubt". Good faith between the two parties is assumed throughout. The document is there for the memory of both.
Alongside the permission runs a caution about how much of you the work takes. The people praised in Surah an-Nur are those "whom neither trade nor commerce distracts from the remembrance of God", which places the risk in absorption rather than in the trading itself. On where wealth comes from and what it is for, see the verses about money and provision; on what is owed to people you hold some power over, the verses about justice.
2:275 — Those who consume usury will not stand except as one stands who has been struck down by Satan's touch. That is because they say, "Trade is just like usury" — but God has permitted trade and forbidden usury. Whoever receives a warning from their Lord and stops may keep what is past, and their affair rests with God. But whoever returns — those are the companions of the fire; in it they will remain.
2:282 — You who believe, when you contract a debt for a fixed term, write it down. Let a scribe record it between you justly. No scribe should refuse to write as God has taught them — let them write. Let the one who owes the debt dictate, and let them be mindful of God, their Lord, and not diminish anything from it. If the one who owes is of weak judgment, frail, or unable to dictate for themselves, let their guardian dictate justly. Call two men from among you to witness; and if two men are not available, then one man and two women from those you accept as witnesses, so that if one of the two women errs, the other can remind her. The witnesses must not refuse when they are called. Do not grow weary of writing it down, whether small or large, along with its term. That is more equitable in God's sight, more sound as testimony, and more likely to keep you free of doubt — unless it is an immediate transaction you conduct among yourselves, in which case there is no blame on you if you do not write it down. And have witnesses present when you trade with one another. Let no scribe or witness be harmed; if you do so, it is moral failure in you. Be mindful of God, and God will teach you. God has full knowledge of all things.
4:29 — You who believe, do not consume one another's wealth among yourselves wrongfully — only through trade by mutual consent. And do not kill yourselves. Indeed, God is ever merciful to you.
11:85 — And my people, give full measure and full weight in fairness, do not shortchange people of what is theirs, and do not roam the earth spreading corruption.
17:35 — Give full measure when you measure, and weigh with an upright scale. That is better, and fairer in outcome.
24:37 — men whom neither trade nor commerce distracts from the remembrance of God, the keeping of prayer, and the giving of zakat — they fear a day when hearts and eyes will be overturned,
62:10 — Once the prayer is complete, disperse through the land and seek God's bounty, and remember God often, so that you may flourish.