Clause 8.4 of ISO 9001 requires the organization to determine criteria for the evaluation, selection, monitoring of performance and re-evaluation of external providers — and to keep evidence of it. In practice this is solved with two instruments: qualification (the entry assessment, before buying) and the periodic performance evaluation, usually consolidated in the SQI (Supplier Quality Index), calculated per supplier every six months.
The classic index weighs three dimensions measured with data from your own system: quality (typical weight 50% — batches accepted / batches received, discounting supplier nonconformities); delivery (30% — on-time deliveries / total); and service (20% — response to quotations, handling of problems, correct documentation — assessed with a simple rubric by the buyer). The rating bands drive the action: above 90% approved; 75-90% approved with reservations (improvement plan); below 75% critical — formal development or replacement.
Two common mistakes: evaluating by impression ("the sales rep is attentive") instead of using receiving data; and calculating the index and doing nothing with it — the score is only worth something if it triggers a consequence: formal feedback to the supplier, an improvement plan with a deadline, or the search for an alternative. A critical supplier that is also a monopolist deserves special treatment: a low score changes nothing if there is no alternative — that case goes into the risk matrix with an action to develop a second source.
The template below shows the consolidated half-yearly evaluation of a manufacturer. Send the result to each supplier: transparency turns the evaluation into a relationship tool instead of internal paperwork.