Identity before price
Start with identity. Know the legal entity, the jurisdiction, and who owns it. Do not negotiate with a name that cannot produce corporate documents, and do not treat a website as KYC.
Trader and producer are not always the same file
Separate the trader from the producer when they are not the same. If the performing mill or plant matters for sanctions, quality or origin, that entity has to be named and screened, not only the company raising the invoice.
A lot that can be described can be compared
Ask for a file that can be inspected: specification, typical certificates, packing, and a delivery window the seller will put in a contract. A supplier who cannot describe the lot they intend to ship is not ready to be compared on price.
Put risk allocation in the terms, not in chat
Write the allocation of risk into the commercial terms: Incoterm with a named place, payment instrument, inspection rights, and what happens if documents or cargo fail. Informal WhatsApp confirmations do not survive a claim.
Do not skip sanctions and end-use. A cheap cargo that cannot be banked, insured or discharged is not cheap. Screening belongs before the quotation is treated as a basis for a contract.
Keep the reasons as well as the papers
Finally, keep the paper. Approvals, rejections and the reasons for both are how a later dispute is reconstructed. A buyer who cannot show why a counterparty was accepted will have a weaker file if something goes wrong.