I just came across this fun article at The Motley Fool: 12 Easy Ways to Devalue Your Home (it’s from some time ago, but is still relevant), which highlights some of the things that can lead to potential buyers knocking down their offers for your home.
My favourites from the list were the fashion disasters of stone-cladding / pebble-dashing, and having garden gnomes, which supposedly together could knock off as much as £3500, as well as seriously ruining your street-cred.
It’s a useful list, as there’s things in there that I would never have thought of, such as having carpet in the bathroom or kitchen (unhygenic).