First, the shape of the problem. In a back-to-back, the seller performs against your purchase credit; you then take his documents, swap your invoice in, and perform against the sale credit. So the purchase credit must be tighter than the sale credit at every point: earlier shipment, faster presentation, every document your buyer demands, and cargo your buyer cannot refuse. A defect here lives in neither credit — it lives between them, and nobody holding only one of them can see it. That is why these eight survived two sets of professional eyes.
1. Latest shipment date (44C): the seller may ship after your own deadline
If the seller uses the five days your credit gives him, the bill of lading he hands you is already outside your sale credit — you have paid for a cargo you cannot present. Fix: amend the purchase credit's 44C to your own deadline or earlier.
2. Presentation period (48): zero days to turn the pack around
The subtlest one on the list. The seller has exactly as long to present to you as you have to present onward, which leaves you zero days to receive his documents, check them, substitute your invoice and lodge the pack. Both credits look impeccable alone; together they are arithmetic that cannot work. Fix: shorten the purchase credit's field 48 so you keep clear days — five is a working minimum.
3. Expiry (31D): paying under a live credit while yours is dead
The seller can present on the very day your own credit dies, or after it. You would be paying him under a credit that is still alive while the credit that pays you has expired. Fix: purchase expiry comfortably before sale expiry, never after.
4. Certificate of origin (46A): your buyer demands what your seller never owed you
Your buyer's bank will refuse the pack without it, and nothing obliges the seller to hand it over. You cannot present what you did not ask for, and by presentation time your leverage over the seller is gone. Fix: every document in the sale credit's 46A must appear in the purchase credit's 46A.
5. Tolerance (39A): 10% in, 5% out
The seller can load five percent more cargo than you can invoice under your own credit. You pay for every tonne and cannot draw for the excess. Fix: purchase tolerance no wider than sale tolerance.
6 & 7. Quality limits (45A): cargo he may deliver, and your buyer may refuse
The gap between those numbers is cargo the seller is entitled to deliver and your buyer is entitled to refuse. Whoever wrote the two specs never read them side by side. You would own that cargo, at sea, with a margin already spent. Fix: purchase spec at least as tight as sale spec, parameter by parameter.
8. The spec your buyer has and your seller has never heard of
Nothing in the purchase contract obliges the seller to deliver cargo that meets a parameter he was never shown. The whole of that risk is yours. This is the same defect as #4 wearing a lab coat. Fix: mirror every sale-side quality parameter into the purchase contract at signature, not after.
The one that almost made it nine
Transhipment: the sale credit prohibited it, the purchase credit was silent — and a silent credit does not prohibit anything. A transhipped bill of lading would satisfy the purchase credit and be refused under the sale credit. It escaped the fatal list only because the route made transhipment unlikely, which is a bet, not a control.
What this says about process
None of these defects requires exotic knowledge to catch. They require reading two documents against each other, term by term, on the day the draft arrives — which is precisely the work that never happens on a busy desk, because each credit alone looks fine and the deadline is always closer than the discrepancy. The cheapest moment to fix any of these is before issuance, when the cure costs an email. At presentation, the cure costs a bank fee, an amendment cycle you may not have time for, and the leverage you no longer hold.
We built this check into opsPhlo Lite: paste both credits and it reads them against each other and against the contract, writes the findings in plain trader English, and drafts the amendment request. The Standard product is free for life for the first 10 companies that sign up — work email, no card, minutes to a working system. Put one of your own structures through it; the eighth finding is usually the one nobody in the chain had read twice.