Interesting. I normally purchase items on Audiogon, US & Canuck Audio Marts (CAM), and even eBay. Selling, I usually just list on CAM.
Checking my history, most of my purchases occur about 50/50 on CAM/USAM or eBay. Most of the time I'm not in a hurry, so I just wait for a good price. However, items that list for a good price sell very fast, often within a day or two. Usually I'm too slow to buy these, and kick myself that I didn't act quickly. In other words, they sell before I complete my due diligence.
The three items I listed on CAM in March all sold within 3 weeks. All three went to local buyers. So my experience is that price and local sales are huge factors.
I also agree that the market is shrinking, i.e. demand is shrinking. So that implies you will have to lower your price expectations when selling.