Once, when I was holding a garage sale which brought in a little money but was lots of work, I overheard a youngish man saying, "Older people always think their stuff is worth a lot more than it is." Maybe that's because our "stuff" has lots of sentimental value for us, which is obviously not a factor for those who are buying. I did find that making prices very low helps to move things along.
But, as Seabreeze says, sometimes it's easier to just donate it and take the tax deduction. Here, we have a wonderful charity called A Wider Circle, which helps people who have been abused, or just battered by life, to get a fresh start by setting them up in a decent home with good, clean, used furniture. Another good charity is S.O.M.E. (So Others May Eat). Both of these groups send volunteers to pick up donated items.
After my husband passed away, I found it almost impossible to give away a hospital bed. Even the nursing homes wouldn't take it (it had been used!) When you go to a hospital or nursing home, aren't the beds used? What a dumb rule! Finally, the Lions Club came through and accepted it. They take wheelchairs also.
