For location it’s common for a property to be in a generally desirable area, but situated right next to a freeway (noise and bad for health) or located right on a busy street (not quite as bad as a freeway, but in certain cases it could be difficult to even get out of your own driveway).

For floor plan, the biggest offenders I’ve seen are configurations that limit the usability of the space.

Narrow bathrooms and kitchens that feel almost claustrophobic. In one case I saw a bathroom that was barely wider than the toilet! I’ve seen kitchens that two people cooking would barely be able to maneuver around. I’ve seen bedrooms that are basically closet sized, which is strictly worse than just having one less bedroom. I’ve seen large lot sizes, but half the lot is on a slope and not able to be used as a backyard.