There are a few things that de-value a home the most that you should be aware of.
Poor Maintenance & Neglect: This is one of the biggest contributors of a decline in value of a home. Signs of deferred upkeep such as a leaking roof, peeling paint, rotting baseboards, mold, outdated electrical, plumbing and HVAC systems scare off potential buyers during a sale. This allows buyers to negotiate lower prices, or just look elsewhere.
Over-Personalization & Customization: Recall when we're selling a home, we want to appeal to the largest buyer set - ones who want move-in ready spaces that they are familiar with and can envision themselves using. Too much customization limits the appeal to buyers (therefore you're only marketing to a very specific buyer, who may or may not be in the market). Unusual uses of rooms (converting a bedroom to a gym, closet, or painting with bold colours) limits the attractiveness of the home. Just because it works for you doesn't mean it will work for 90% of the buyers who we're marking to.
Location-Related Issues: Some issues are out of our control. Be realistic with comparable sales that you're reviewing; do they share similar location-based features? Close to industrial, neighbourhood decline, types of homes, street style, curb appeal, even the types of trees lining the street can impact it's attractiveness.
Poor Quality Renovations: Not all improvements add value. Ever seen a hot tub in a living room? I have. Not a great idea for a buyer. Although with a high 'cool' factor, it has a very strong negative 'salability' factor. Shoddy craftsmanship, low quality materials reduce the attractiveness of the home and leaves the buyer with more questions than answers.
Neglected Curb-Appeal: Curb appeal is the first thing buyers see when they drive by. We want to create a sense of intrigue in the right way. Overgrown lawns, dead patches, weeds, cracked driveways, peeling paint, faded siding turns buyers off. "If the outside looks like this, how bad is the inside?" is the line of thinking here.