PeptideChemSF said:

Concentration choice is a precision decision, not a preference.

I am going to disagree with reconstituting low as a general rule. More diluent, more punctures, more in-use days at room temperature, and the stability trade-off is real. Precision is not the only variable being optimised.

Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

Adding the numbers, since they settle part of this. Red flags, in rough order of how much they should worry you: no verifiable address, no batch numbers, prices far under market, vendor-commissioned tests only, pressure toward irreversible payment, and shipping with no temperature control.

NeuroNate said:

I am going to disagree with reconstituting low as a general rule.

There is a second half to this that has not been said yet. Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion. Synthesis, testing, and cold-chain shipping have floors. A price well under the floor means something was skipped, and the two things that get skipped are testing and content.

Worth separating that from vendor vetting, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

A narrower follow-up, since the general answer is now clear:

How to check the arithmetic without trusting a website calculator, since three calculators gave me three answers?

Reporting back.

Follow-up: it was dead space. Switching to a low-dead-space fixed-needle syringe gave me the tenth dose back.