The sample was perfect. The 5,000 units that showed up were garbage. This is the single most common way sellers get burned, and it has a boring, fixable cause.
A golden sample is one physical unit you approve, sign, and write into the order as the standard the bulk must match. It turns "we thought it would look like the sample" into a contract term.
Photograph it, tag it, and keep one. The factory keeps the matching one.
Bulk production must match the approved and signed golden sample in every respect.
Pay 30 percent to start. Hold the 70 percent until a third-party inspection confirms the bulk matches the golden sample.
Firms like SGS or Intertek inspect before you release the balance, usually for a few hundred dollars. Now the factory eats the mistake, not you.
That one page of paperwork is the difference between a bad batch and a bad year.