The single most cost-effective quality check — before the goods leave China.
A pre-shipment inspection checks a finished, packed order — usually when 80–100% is produced — against your spec and an AQL sampling plan, before it ships and before you pay the balance. It is the single most cost-effective quality check in China sourcing, because it catches defects while your money and your leverage are still in play.
A pre-shipment inspection (PSI) is a final check of a completed order, done when it is 80–100% produced and packed. Timing matters: too early and there is nothing to inspect; too late and the goods have shipped. The PSI is scheduled just before shipment so any problem can still be fixed or the shipment held.
An inspector does not check every unit — they pull a statistically valid sample using an AQL plan and count defects by class (critical / major / minor) against agreed limits. This gives a reliable accept-or-reject decision from a sample, in a day, at a fixed cost.
PSIs are performed by independent third-party agencies for a fixed per-day fee. The highest-value move is to tie your balance payment to a passed PSI — you release the final payment only once the report confirms the goods meet spec, so quality problems are the supplier's to fix, not yours to discover on arrival.