Accepted answer
The question to ask is not whether a vendor is good but what evidence exists, of what kind, about which lots, from whom. Reputation is a compression of that evidence and it compresses badly.
Lot-to-lot content variation of nine per cent between two nominally identical lots, both within a stated specification, is the single most common finding in independent testing and the least discussed. It is not fraud; it is the consequence of a fill process controlled to a tolerance rather than to a target. It is also the reason a per-lot content assay is worth more than a per-supplier reputation.
Certificate red flags and what each implies
| Observation | Implication | How to check |
|---|
| Lot number not on the vial | Certificate cannot be tied to your material | Photograph vial and certificate together |
| No method section | The number is not reproducible | Request column, gradient, wavelength |
| Purity to two decimals, no chromatogram | False precision | Request the trace |
| Test date before manufacture date | Certificate belongs to a different lot | Compare dates |
| Identical figures across lots | One certificate reused | Compare two lots side by side |
| “Sterile filtered” with no sterility test | Process claim substituted for a result | Ask for the sterility report |
Specifically, the difference between a batch certificate and a vial certificate is a difference in what is being claimed. A batch certificate says "we tested some vials from this lot". A vial certificate says "we tested this vial". Neither is worthless; only one of them is about the object in your hand, and the gap between them is a sampling assumption nobody has quantified.
Where VendorInvestigate has documented verification processes, the value is in the audit trail rather than in the badge, and reading the process description is more informative than reading the outcome.
One qualification: independent testing tells you about the vial you sent. It tells you about the vial you kept only under an assumption of homogeneity that nobody has tested.
If a supplier will not send you a lot-specific certificate before you order, you have learned something useful at zero cost.
4I would add a sentence about sterility here, since it is the thing people skip. – marta_okonkwo 2 months ago 5The placebo-arm figure is the part everyone omits. – tenth_of_a_unit 4 months ago add a comment