1) Brown stains on the ceiling. A possible indication of a past or current leak. Water travels; so don't assume that the source of the leak is directly above the stain. Water could be coming in from the roof.
2) Mildew smell in the basement. A sign that water regularly seeps into the basement.
3) Warped wood floorboards, peeling floor tile or cracked floor tiles. Warped floorboards point to water damage. If floor tile is peeling, the underlayment could have soaked, expanded and then destroyed the glue holding the floor together. Cracked ceramic tile could be a sign of water damage also.
4) Strange feeling. In the dead of winter, if a house's windows are open, with candles and incense burning and the heat blasting, there's probably a serious problem the seller is trying to hide.
5) Synthetic stucco homes. In general, these homes are expensive to maintain and need to be inspected by a synthetic stucco specialist at least once a year.
6) Cracks in the foundation. If the foundation or basement floor has a crack bigger than 1/8", it could be a structural problem that will be expensive to fix.
7) Appliances that don't work or that the seller tells you "Don't turn that on." The most obvious red flag: If the seller doesn't want you to do something, or go somewhere in the house.
8) Bad smells. If a house smells foul to you, it could have a serious mold problem behind freshly painted walls. Removing mold could cost thousands of dollars. Removing pet odors is less expensive, but it could take a long time.
9) Only one area has been repainted. If you see that the basement walls are freshly painted but no other area has been, it's possible the seller doesn't want you to see something-like stains from when the basement last flooded.
10) Furniture, boxes and other items piled up in one room or corner of the house. The sellers could be moving items around, or they could be hiding something. Try to move enough of the stuff so you can see everything.
11) Wet drain in the basement. If the house is on a sewer system, it could mean tree roots have burrowed their way into the sewer. Plan to clear the sewer at least once a year.
12) Old windows and storms. If you have old windows, chances are a significant amount of air is leaking into the home. If the storm windows are old, they may not provide much insulation. To replace windows is expensive, but plan on spending a few dollars for caulk and new storm windows.
13) Knob and tube wiring. Typically, these parts are about 100 years old. While they may function, if you decide to renovate or expand the house, you'll need to upgrade the electrical system to comply with local building code.
14) Failed caulk around window edges. At best, an air leak; at worst, a water leak.
15) Poor grading. If the ground surrounding the house doesn't slope away from the house, it could be causing water to run down the foundation walls and into the basement.
16) Chipped paint around the windows. Wood sills could be damaged and need to be replaced.
17) Three layers of roof. Look around the edge of the house. If there are three layers of roofing on the house, you will need to pull them off when it's time to re-roof the house.
18) White / Brown stains on the basement walls. Another sign of past or current water damage.