Advice - post machining finishing of brass and Aluminium

Hello, long time lurker first time poster. Please let me know if this is the wrong place or there is a better place to post this.

I design a number of products, mostly fabricated in Australia, recently due to quantity I have started manufacturing two of them in China. CNC milled out of brass and Aluminium.

I have asked the fabricators after machining for these pieces to be vibration polished, sample comes back fine but when it comes to a production run, the exterior faces have been ‘polished’ with a 320 grit orbital sander. None of the interior faces have been polished and it’s covered in grime.

Would you have any advice or direction for specifying/communicating this to a O/S manufacturer?

I have supplied them a step file of the design, a detailed drawing with annotations and photograph of the finish. Am I missing anything or is there a better way to specify this?