Sunglasses sold in Europe must carry CE marking to EN ISO 12312-1; in the United States the reference is ANSI Z80.3; in Australia and New Zealand AS/NZS 1067 is mandatory. All define UV transmission, optical quality and the filter category from 0 (clear) to 4 (very dark, not for driving).
UV400 is the market term for full UV blocking. Polarised lenses add a film that cuts reflected glare; the film is laminated inside TAC, CR-39, nylon or glass lenses. TAC polarised sheet is cheapest and dominates volume sunglasses; nylon and glass are premium.
Category 3 is the normal sunglass. Category 4 is for glaciers and deserts and must be labelled as unsuitable for driving. Ask the factory for a test report against the standard for the market you sell in, and for UV transmission figures, not just a UV400 sticker.