Savvy home buyers know that when they’re checking out a house, they should kick the tires—or maybe the floorboards, bathtubs, and walkways—to ensure everything is in working order and they don’t end up with a housing lemon. Sure, you’ve probably heard that you should turn on the shower to check the water pressure. It’s true! But there’s way more you can do to avoid an unpleasant surprise later on that may require expensive repairs.

Take your sneaky investigative skills to the next level with these quick and easy expert tips to see if a home is actually worthy of an offer.

Use your marbles

Here’s a simple (and fun) tip to find out if the floor is tilted: Place a marble on the surface, and see if it rolls.

“Sloping floors could be signs of a charming old house or a more serious condition with the foundation,” says Randy Sipe, president of the American Society of Home Inspectors. In other words, proceed with caution and have this vetted by a home inspector before you get too serious about this place.

Snap pics of serial numbers

Whip out your smartphone and snap pictures of the serial numbers of large appliances, then Google them later for details. In particular, you can learn how old they are—something that otherwise might not come out until disclosure. You might be amazed.

Note: A water heater’s number is right on front; ditto for a furnace or HVAC unit.

Look up

No matter how thoroughly you ogle the kitchen and closet, don’t forget to also look up.

“Inspect the ceiling for water stains, which are signs of a leaky roof,” says Sipe.

A fresh paint job should also set off your internal alarms, since paint can do a fine job at hiding water stains underneath. Go ahead and ask if there’s been any water damage; homeowners in most states must disclose many underlying problems. It’s the law.

Open, close, repeat

“Open and close doors to see if they shut smoothly or bind and don’t latch, indicating signs of excessive settlement,” says Sipe. Off-balance door and window frames—the cause of sticking—are classic signs of a possible foundation problem.

Go outside and walk in a circle

While it’s tempting to spend all your time checking out the inside of a house, make sure to check the outside, too.

“Water damage can lead to expensive repairs and mold infestation,” says Ryan Larsen, a civil engineer at NDS and known as “Dr. Drainage” on his YouTube video series. “Home buyers need to ensure that drainage is sufficient on any property.”

Larsen suggests checking to see if the ground directly adjacent to the foundation slopes away from the house, or toward it. Grading that slopes toward the home could lead to damp crawl spaces, structural damage, and toxic mold. Next, find the rain gutter downspouts. Do they drain directly to the ground, and is there a low spot for water to collect near the home? If so, “there’s a good chance there’s water intrusion somewhere.” Downspouts should carry water at least 10 feet away.

Whip out your credit card

All foundations include a few tiny cracks, but which ones are really worth worrying over? Sipe offers this insight: “Look at the foundation for any cracks larger than the thickness of a credit card, which could signify water leakage. Pay special attention to corner areas, since cracking there may be signs of movement, which may require repair.”

Open the curtains

“Oftentimes a window is foggy from condensation if the double-pane window seal is defective and leaks,” says Realtor® Judy Chin.

Touch the walls

Ease your water seepage concerns by heading straight to the basement and checking the base of walls for water marks. If there’s a lot of moisture, the walls may even feel a bit soft.

Take some video footage

Can’t fit into a small crawl space or cramped attic? Deb Tomaro, a Realtor in Bloomington, IN, advises potential buyers to at least stick their arm in and videotape the area with their phone. “Then you can download the tape onto a computer and zoom in to get a good look.”

Arm yourself with a few apps

Apps abound that can help when checking out a house. For instance, did that ad say “sun-drenched master bedroom,” but you’re visiting in the evening or on a cloudy day? Don’t take their word for it; download the Sun Seeker app, which will tell you when (and if) certain rooms will get sunlight throughout different times of the year.

Is the home in dire need of a paint job or refinished floors? The Handy Man app will calculate how much you’d have to spend to redo a floor or paint a room. That way, you have a sense of how much these renovations will cost and can plan accordingly.