Most problems in a first shipment are not quality problems. They are expectation problems. The buyer pictured one thing, the supplier quoted another, and nobody wrote it down.
Grade, size, moisture content, admixture, packing weight. Get all of it on the proforma invoice. A sample is useful, but a sample without written tolerances is an argument waiting to happen.
FOB and CIF are not interchangeable. Under FOB your responsibility begins once the goods are loaded. Under CIF the supplier arranges freight and insurance to the destination port. The price difference is not profit, it is scope.
Pre-shipment inspection should happen before the container is sealed, not after it lands. Ask for photographs of the loading, and ask whether a third party agency is welcome. A supplier who says no is telling you something.
Certificate of origin, phytosanitary certificate, packing list, bill of lading. Ask which documents your customs authority requires and confirm the supplier can produce all of them before you pay a deposit.