Anyone who has been in this business for a while knows that pricing a home isn't always easy. There are so many factors that come into play, in addition to the comparable sales, such as the ages of the furnace, central air, hot water tank, windows, roof, and driveway, just to name a few. Theses items I mention I often refer to as "big ticket items" because they can cost thousands of dollars.
Many sellers choose to sell their homes to avoid having to replace any of these items, which I completely understand. However, it's important to recognize, that a buyer will factor that in when they make an offer. If the new buyer is planning on 10 or more years in the home then they know they will likely have to replace many of these items. They will likely make an offer that is lower to account for the upgrades they may be forced to make.
To be clear, I am not suggesting that sellers replace mechanical systems that are working just fine, but they should be realistic that older systems should be factored into the list price.