That is very disturbing and has somewhat soured me in buying a Chinese DAC. I was going to buy a Holo Audio May today but may need to rethink my options. Even though your problems were with Audio GD, they have no control over Chinese Customs.
Be careful, as you are conflating in a manner that may restrict your choices unnecessarily. I am not aware of any similar stories relating to Denafrips or Holo Audio, to pick two obvious examples, and doubt very much that anything similar would happen if a return were necessary.
It is damning that Audio GD behaved as reported, and I wouldn't go near their products because of that alone. But while I have moved on from a Denafrips DAC, my dealings with Alvin, their worldwide representative, based in Singapore, were comparable to the positive experiences that I have had with American and European companies.
If you are interested in a Holo DAC, why not contact them and ask specifically how returns would be handled. My bet is that you wouldn't be on the hook for any Customs charges, even if it were necessary to ship the unit back to China.