Not sure what the point is... Some things that are in high demand, like the Ti Canon mount or DSMC Side Handle, are often being sold at a premium. Now I think that asking double is kinda messed up, I've known plenty to sell at about regular price. Shop around, it's not like they're that scarce or hard to find. If you don't like the price that someone is asking, then don't do business with them. Problem solved.
Likewise, having just been through selling a RED One camera, the vast majority of offers or inquiries I received were ridiculously low. At first I was shocked when the first offer rolled in, offering $7K for what normally sells used for $25K and would cost nearly $48K new... By the time I sold the camera, for a reasonable price, I had received so many of the low-ball, please help out a starving film student offers that I was totally desensitized of it. And even though I held out for a reasonable price, it was just that, reasonable. It probably should have sold for more, but there's a lot of people out there who are apparently desperate to sell such things. ...Supply and demand. As Joel says.