How will the COVID-19 pandemic affect sites like Audiogon?

I think, people are afraid. Fear can manifest itself in different ways, including aggression, both verbal and not. I also think people are confused and most are completely unprepared for possible big changes, hopefully temporary. 
40% unemployment may sound like exaggeration, but this is a new situation so who knows ? Surely can be 20%, I would guess.
Stratification of the society should increase too - good if I am wrong.
As for buying equipment, right now I am not in the mood and I upgraded last year. Sure, many will be saving up and buy nothing , degree of uncertainty is high.

Canada should be prepared for the 'American virus' to come to them. No, you can't close the border. I know where to cross it in a broad daylight undetected, and so do many others. Americans will come for healthcare too if it becomes a madhouse here. And, finally, we can invade Canada and overrun it in two weeks or less if needed. Stay alert.

Let me just say..you got it right. I don't know about Canadians but if pushed hard enough Americans will come and take.

There is, I would guess. Some European brands at least.