When searching for a new home, looking for indications of water in the basement is about as common as kicking the tires of a used car -- everybody does it, but few have any idea what they are really looking for, or why.
A wet basement can be more of a problem than simply the loss of usable utility space. For the typical wood frame home, chronic basement dampness can increase the potential for structural rot and wood boring insect infestation. The potential impact of a wet basement is even greater in many newer homes where lower air infiltration rates (or "inadvertent ventilation") increases the time exposure of the structural framing to moisture. Moreover, many newer framing materials, such as plywood truss joists, have a much lower resistance to a moisture-induced loss of strength.
So what should we be "kicking" in the basement?
Start with how the owner stores basement goods. Are they on wood pallets, or joists, or anything else that appears to be intentional to protect stored goods from water on the floor? While some homeowners may just be unduly fastidious, a seller's raised storage should raise a prudent buyers suspicions.
Take a deep breath -- smell anything musty? Look for actual water marks near the base of the foundation walls and at the bottoms of the stair carriages.
Next, look for more subtle signs of a water problem. The salt-like crystalline deposits which sometimes form on the inside face of foundation walls, known as efflorescence, may indicate a water problem (but may also indicate only mild dampness in the foundation).
If the basement floor has resilient floor tile, look for loose or "popped" tiles. Loose tiles are often a good indicator or water exposure.
Finally, get a look inside the base of the furnace cabinet, where the filter and blower are. Take off the blower cover and look closely for rust near the floor with a flashlight. Even the most deceptive home seller trying to conceal a water problem will almost always forget to paint the inside of the furnace!
The good news is that If you have, or are about to acquire, a wet basement, resolution of the problem is often easy and inexpensive. The substantial majority of wet basements are wet because of poor surface drainage near the foundations and/or poor water discharge from the roof drainage system.
No foundation is as water-tight as the hull of a ship. If the ground which is in contact with the outer face of the foundation is chronically saturated, water will eventually find its way through any type of foundation. Get outside during a heavy rain and actually observe how the water flows from the roof drainage system -- you may be surprised how obvious the source of the problem is. Correction of a wet basement is often as simple of redirecting or extending some downspouts, or improving the grade (the slope of the soil surface) so that water flows away from, instead of towards, the foundation.
There are, of course, many homes where the water source is not overt and the services of a water proofing professional are needed.
However, the frequency of unnecessary basement "waterproofing" is well exemplified the waterproofing contractor who spoke a few years ago to a group of home inspectors.
After a well-presented 40 minutes discussing state-of-the-art water collection systems, the contractor was asked by one of the attending home inspectors: "Don't you find that in most cases, a water problem a home owner asks you to fix is attributable to some simple exterior drainage condition?" To which the contractor incredulously replied: "Well...yes. But I could hardly make a good living by installing downspout extenders!" The room was silent!