Most "factories" on the big marketplaces never touched a machine. They are trading companies, middlemen who mark up a real factory and forward your emails. Here is the 60-second test.
A middleman adds a layer for doing very little. Factory makes it for a dollar, the trader adds thirty cents, you pay the thirty cents forever. On a real order that markup is the difference between a healthy margin and a thin one.
Every registered supplier has one. If the business scope says trading, wholesale, or import and export, and does not mention manufacturing or production, it is not a factory.
Not a polished file they email you. A real factory can walk the line on a live call in about five minutes. A trader stalls, says the engineer is busy, or sends a recorded clip.
A real factory answers instantly and specifically. A trader goes quiet, because they do not know.
Stalling equals trader. Instant, specific answers equal factory. Run this before you wire a deposit, not after.