Real estate is local, of course, and I have noticed certain things over the years that make a house stubbornly cling to its sellers instead of taking in new owners. At least in my area, and maybe in others, these issues can cause the house to take longer to sell.
One of them is blue carpet, as per my soon-to-be trademarked slogan in the title of this post. Emerald-green carpet isn't great, but it's not as bad as blue. (Below is an actual photo from the MLS.)

Another thing that keeps houses from selling is bad feng shui that comes from having the stairs start right in front of the front door and continue straight up to the second floor. My Asian clients often comment on this.
The stair thing isn't too much of a problem for one-story houses. But they, like two-stories, can be affected by bad chi, which happens when the house is located where a street comes to a T-intersection in front. I think that the chi rushes up the street and blows right into, through, or against the house. Houses directly at the end of cul-de-sacs are affected, too.
Home buyers don't like puzzling rooms, either. I showed a vacant house recently in which the garage had been partly converted to a room. There was still a garage-type door to the room in the hallway, and another garage door at the other end of the room into the garage. There were no windows. There was a cedar-lined walk-in closet. The floor had the same new carpet as the rest of the house. There were 8 large fluorescent light fixtures on the ceiling. And all around the room at about 3 feet apart and 3 feet off the floor, there were electrical outlets. They were in the closet, too.
What was up with that room?! It would make a perfectly good game room or media room, once the fluorescent lights were replaced and a new door installed, and it wouldn't cost much. But I think that room may have too many strange little quirks for buyers to be able to imagine the possibilities.
What strange things have you discovered that keep a house from selling?
I am with you...I can't stand blue or green carpet. Or how about orange formica countertops? I mean really?...can we say "OUTDATED!!"