Short answer. It is presumed. The Rules presume that private transactions have been fair and regular, so you do not have to prove regularity as part of your own case. Whoever alleges irregularity or bad faith must prove it, and the presumption yields once contrary evidence is in.
What the law says
That private transactions have been fair and regular
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
What the law says
That the ordinary course of business has been followed
Rule 131, Section 3 — Disputable presumptions. Read the full provision →
The presumption and its companion
Section 3 of Rule 131 presumes that private transactions have been fair and regular, and immediately after it, that the ordinary course of business has been followed. The two work together. The first addresses the character of a dealing between parties; the second addresses the way it would normally have been carried out. Between them they mean that a party relying on an ordinary transaction is not required to begin by proving that nothing improper happened, which would be a difficult thing to establish and an odd thing to demand.
What it does to your case in chief
The practical consequence is about what you must prove to make out your claim. You establish the transaction itself, its terms, and whatever performance or breach you are relying on. You do not have to add a separate showing that the dealing was fair, that no one was defrauded, or that the usual steps were taken. Those are matters the presumption supplies. It is the party asserting fraud, bad faith, or irregularity who must plead and prove it, and generalised suspicion does not discharge that.
It is a default, not a shield
Like every presumption on this list, it is disputable: satisfactory if uncontradicted, but capable of being contradicted and overcome by other evidence. So it is a rule about where the court starts and who has to move, not a rule that protects a transaction from examination. Once evidence of irregularity is before the court, the presumption no longer decides anything and the issue is resolved on the evidence. A party cannot rely on the presumption to avoid answering proof that has actually been presented.
Where other rules take over
This presumption operates against a general background, and other provisions of law can set a different starting point for particular transactions or relationships. Where a specific rule imposes a heavier burden of justification on one party, that rule governs the point it addresses rather than this general presumption. So the useful question in a given dispute is not only what Rule 131 presumes, but whether the transaction falls under a provision that speaks to it directly. That is a question worth putting to counsel with the documents in hand.