My other thought is that the seller is doing himself no favours as far as future sales are concerned as I'm sure we are all fully aware of who he is and will be avoiding any future sales like the plague.
It might even be the case that something happened in transit, I had that with a Bluesound Node 2 streamer that arrived faulty, took me a lot of testing to try and diagnose the problem, I never did find the cause at my end but the seller took it back and sent it to Bluesound who had to replace the main board and it cured the issue right away. He then sold it elsewhere as I didn't trust it arriving back here safely again.
But that was the benefit of a genuine seller who was prepared to help out a genuine buyer with an item that was perfect when sold but was damaged internally in transit. It might be a similar case with the Opus.