Why does every GHRP-2 vendor claim exactly 99% purity?

If you want to check this yourself, ask the vendor which laboratory issued the certificate, then email that laboratory with the report number. Most will confirm or deny. The ones that go quiet tell you something.

If your solution went cloudy after reconstitution that is usually either the diluent or the temperature it was stored at. Worth posting what you used.

Same.

To answer the methodology question directly, Purity & Testing carries 25% because it is the dimension we can measure most reliably. The full weighting is published on the methodology page.

Batch-to-batch variation is the thing people underestimate. A passing result certifies one lot, not a product line, and vendors know most buyers do not make that distinction.