I would split this between Dealers who are offering products that are Demos or lines they actively carry vs. hobbyists. Some manufacturers have rules in how you list used goods. Some prohibit it altogether. You follow the rules or lose the line.
In the end, a listing is just based on what the market will pay. I just listed a used Hegel H390 (I am not a hegel dealer) for 20% off. It sold in 2 hours at a small discount from that. I look at recent sales in the Bluebook, other listings (TY HiFi Shark) and prices are driven by those recent sales.
You can complain about the prices but if stuff is selling...
In the end, a listing is just based on what the market will pay. I just listed a used Hegel H390 (I am not a hegel dealer) for 20% off. It sold in 2 hours at a small discount from that. I look at recent sales in the Bluebook, other listings (TY HiFi Shark) and prices are driven by those recent sales.
You can complain about the prices but if stuff is selling...