A follow-up to Tom Reichner's post, above. When I list something relatively new, I first check Canon refurbished. If it is available there (not everything is), I undercut that price by 10-15%. People buy used to save money, DUH! My next step is to search that item on the FS boards here. For example, I saw 5 active, open listings for 70Ds. I believe the lowest price was $750, body only. High? Maybe $850. Canon sells it refurbished for $699. I added a lens (18-55 STM to sweeten the deal, and listed it $50 below the cheapest active listing. After two days with no action (I still hadn't posted photos yet), I added a 270EX II unit to the listing. In less than an hour, I got a full-price offer for the package. The entire point of listing an item is to sell it. The stuff I list sells.
If I am selling something that is NOT available refurbished, I check E-Bay "SOLD" listings, average the last 10 sales, and undercut that by 10%. The internet allows me to advertise to the entire country. The price I pay for that is S&H, and PP fees. That is just part of doing business. If you want to sell something, price it like you want to sell it. If you want top dollar for your used stuff, be ready to sit on it for awhile.
Perhaps sales are slowing down, here. I'm not seeing it. Everything I list sells. Price it right. They will come.