In business transactions, both buyers and sellers usually agree on a product specification and acceptance criteria for the items being purchased. These criteria may include things like full functionality, dimensions within tolerance, intact packaging, and no defects in color or appearance. However, some acceptance criteria are hard—or even impossible—to quantify. Examples include sink marks on plastic parts, gloss or color tone after painting, or appearance issues that are judged mainly by visual feel. So how should these be defined?

To deal with these kinds of quality issues—or to align with real-world process capability and improve yield (and reduce cost)—the seller will often provide samples that represent the minimum acceptable quality level during production. If the buyer agrees to accept this minimum level, they will sign off on the sample to show approval. These signed samples are commonly called Limit Samples or Golden Samples (occasionally also called Boundary Samples, though that term is less common). Later, if there is a dispute over these non-quantifiable quality issues, both sides refer back to the signed limit sample as the judgment standard.

That said, when signing off on a limit sample, it’s important to avoid ambiguity. Don’t take shortcuts. Always clearly mark the accepted areas and conditions, not just sign the sample. Otherwise, it’s easy for misunderstandings—or disputes—to arise later.

Key points when approving limit samples:

1. When preparing limit samples, we usually sign at least two copies, and more often three. One is kept by the seller, one by the buyer. Since our products are outsourced, we also sign an additional copy for the contract manufacturer’s inspection use, while keeping one for ourselves. The factory’s copy is typically stored at IQC and used as the inspection reference standard.
2. When signing, the signature, date, and whether the sample is Accepted or Rejected must be clearly legible. In some cases, not only accepted samples but also rejected samples are signed. This helps inspectors better understand the boundary between OK and NG when judging incoming materials.
3. For sample storage, it’s strongly recommended to attach a label showing the part name, part number, accepted characteristics, sign-off date, signer, and expiration date. This makes future traceability easier and avoids confusion.
4. Limit samples must be stored carefully. Exposure to sunlight (even fluorescent light), moisture, physical damage, scratches, or pressure should all be avoided. Otherwise, the sample may deform, fade, rust, or change in appearance over time.
5. Some limit samples are special cases—for example, a waiver that applies only to a specific lot or quantity. These conditions must be clearly marked, and once the validity period expires, the sample is no longer valid.
6. Always mark or circle the accepted areas. When signing, clearly indicate which specific locations and appearance features are acceptable, rather than just signing the sample. Otherwise, someone may later assume the entire product appearance was approved, and any additional defects found on the sample could be mistakenly treated as acceptable.

Today’s photography tools are very mature. For these hard-to-quantify quality standards, it’s highly recommended to take photos as records and include them directly in the specification. This helps reduce reliance on physical limit samples, which are honestly quite difficult to preserve over the long term.

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