Batch numbers that do not match the vial label

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.

Coming back to post #14, because the follow-up matters more than the original answer.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

post #16 answers the question as asked. The question underneath it is different.

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.

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 disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

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.

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.

Pricing patterns: unusually low prices for what are otherwise consistent with market rates might indicate lower quality, stolen goods, or a scam. Unusually high prices without justification raise different flags.

Worth separating two things that post #19 runs together.

Anonymity: a supplier that will not disclose legal name, address, or responsible person is not operating in a way that allows accountability.

post #23 is right about the mechanism and I think understates the practical bit.

Patterns that reliably precede a problem: underdosing (less active material than stated, documented by independent testing), mislabelling (wrong compound, wrong strength, or wrong batch on the label), and failure to provide documentation when asked.

Coming back to post #23, because the follow-up matters more than the original answer.

Inability to trace lots: if you ask "where was this synthesised, by whom, under what conditions" and cannot get a clear answer, that is a red flag. Traceability is not glamorous but it is foundational.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

Unresponsiveness: a supplier that does not reply to reasonable requests for documentation or clarification is showing you something about how they operate.

post #27 answers the question as asked. The question underneath it is different.

Safety documentation absent: a supplier that cannot provide information about sterility testing, endotoxin testing, or safety documentation when asked is raising flags.

Safety documentation absent: a supplier that cannot provide information about sterility testing, endotoxin testing, or safety documentation when asked is raising flags.

This follows post #27 rather than contradicting it.

Anonymity: a supplier that will not disclose legal name, address, or responsible person is not operating in a way that allows accountability.