Well, in the world of sales there are some basic rules that govern the "value" of any item for sale. They sound simple, but they are really useful in understanding why things sell at a certain price. (worked in sales for more than 22 years)
1. Something is "worth" exactly what any one person is willing to trade at any given moment.
Sounds simple, right? Note that this has nothing to do with what you (the owner) paid for it, what you need to pay your bills, how much money you spent fixing it up after you bought it, or any other personal issues you are trying to solve by selling it. The interesting thing to note here is that at any given moment, ten different people might be willing to trade ten different amounts, and any one of those people might be willing to trade a lot more, or a lot less tomorrow or next week. That's because
2. What someone agrees to trade is based on two things: a. How closely the item meets their needs, and b. what options they have to meet those same needs.
Basically just a fancy way of saying Supply and Demand dictate price. Something can be impeccably clean, might've had a lot of money invested, been painstakingly cared for for 20 years, amazingly, none of that matters if nobody has enough interest to trade what you want in return for it at the time you decide to sell it. Crazy, right?