What do you care, what other people sell their items for? If they prefer to sell their stuff quickly, and are willing to make less profit than they perhaps could have, that's their option. And if you think you can exercise enough patience to hold out for a better sell price, then by all means, list your item for what you think is fair. But from the sounds of it, you don't seem all that patient at all. You sound like an amateur who wants to play the market with a get-rich-quick scheme, but are getting frustrated that it isn't happening overnight.

As others have suggested, if you feel that someone is selling something for much less than it could have sold for, go ahead and buy it yourself. Then sell it for higher. If you can.