Inconsistency across documents: a certificate stating one purity, a website claiming another, and a supplier's verbal representation claiming a third, all on the same product, is a red flag for either incompetence or deception. That is the shape of it. The detail is where I would expect to be corrected.
On the subject in the title: A supplier that answers analytical questions with restated claims Working notes rather than a conclusion.
Reading back through what has been written here about supplier, three questions come up every time and only one has ever been answered properly.
Listing all three, with what I think the state of the answer is for each, so the thread can start further along than the last one did.
Inconsistency across documents: a certificate stating one purity, a website claiming another, and a supplier's verbal representation claiming a third, all on the same product, is a red flag for either incompetence or deception.
That is the shape of it. The detail is where I would expect to be corrected.
Adding the measurement that post #2 says would settle it.
Evasion when asked: if a supplier does not clarify when asked specifically for method details, counter-ion form, or batch origin, that itself is a red flag worth documenting.
The opening post describes the usual case. This is about the unusual one.
One more thing on supplier that took me far too long to see: the two figures people quote are not measuring the same quantity. Once you notice that, the apparent contradiction disappears.
Building on post #2 rather than restating it.
Being wrong in public about a supplier is costly to that supplier and to the person who was wrong. That is why the evidence standard is what it is.
Documentation quality as a signal: a supplier that reports method identifiers, distinguishes specification from result, and states the counter-ion form is telling you something about systems behind the document. A certificate that is a number and a signature tells you less.
Answering the question post #4 raises rather than the one it answers.
The guidelines draw that line for a practical reason as much as a fair one: reports accumulate into something useful and allegations do not.
If anyone has run this properly I would rather read that than my own guess.
Coming back to post #8, because the follow-up matters more than the original answer.
On supplier I would separate what is worth knowing from what is worth acting on. The first list is long and the second is short, and conflating them is how threads get heated.
Confirming post #11 from a second method, which matters more than confirming it from a second person.
The strongest single signal available cheaply is what happens when you ask a technical question. A quantitative answer inside a working day is difficult to fake at scale.
This is the first time the answer has come with its own limits attached. Appreciated.
Anonymity: a supplier that will not disclose legal name, address, or responsible person is not operating in a way that allows accountability.
I have changed my mind on this once already, so take it as current rather than settled.
Where I part company with post #11, and it is a narrow parting.
Reporting rather than recommending, on supplier. What happened is above. Whether it should have is a different question and not one I am qualified to answer.
Post #15 is the version of this I will quote in future. One addition.
Rapid supplier turnover: a supplier that changes corporate structure, domain name, or contact repeatedly in short time windows raises suspicion about stability and legitimacy.
I looked this up rather than remembered it, which is the right order.
A stock listing that never changes and a lead time that never varies are both worth noticing. Real operations have variation in them.
If anyone can point at the primary source I would be grateful.
Post #15 put the caveat in the right place and I want to underline it.
Exaggerated claims without documentation: every compound has limits. No peptide is "100% pure" because purity is measured to finite precision. A supplier claiming implausible perfection without backing evidence is overreaching.
I would call that likely rather than established.
That is the distinction I keep failing to hold on to. Written down now.
An unexplained discrepancy that the supplier declined to address is a legitimate thing to record, stated as exactly that and nothing more.
This is where my knowledge stops and I would rather mark the edge than blur it.
The arithmetic in post #21 is right; the assumption feeding it is the part to check.
A supplier changing batch nomenclature is not a warning sign, and it does make historical comparison harder until a mapping exists.
Safety documentation absent: a supplier that cannot provide information about sterility testing, endotoxin testing, or safety documentation when asked is raising flags.
The right answer here may simply be that it has not been measured.
Adding the measurement that post #24 says would settle it.
Distinguishing three things in the supplier discussion that keep getting used interchangeably: the observation, the proposed mechanism, and the recommendation that gets attached to both.
Post #26 describes the usual case. This is about the unusual one.
The strongest argument against my own position on supplier, stated as well as I can state it, since nobody else has yet.
Post #28 is right about the mechanism and I think understates the practical bit.
Where somebody posts a concern, ask what would resolve it before arguing about it. Half of these threads end with a document nobody had asked for.