1. Product specs definition
Before issuing an order, your quality department or your QA service provider should define very precisely what you expect to receive. Describe the product and its performance/resistance requirements, but also the packaging and the labeling. Whenever applicable, set limits and tolerances.

Get the supplier to accept the spec sheets (after discussions and revisions if necessary). And make them a part of the contract.

2. Regular product quality inspections
For new manufacturers of new products, make sure you check quality during production, and again before shipment.

For re-orders, final (pre-shipment) quality control is usually enough. And, for your best suppliers, you might not need to check every shipment.