With a flashlight, look at any piece of metal you can. Don't forget to check the hinges on the doors, the hood and the trunk and their molding areas, as they can rust on them. Finally, look under the trunk carpet. You might be surprised to find a rust stain hidden under there.
If you think a car has been repainted due to rust, be sure to look at it in the sunlight for the best possible view. Look for “bubbles” in the paint. This is a common problem when a car is repainted, but the underlying rust has not been removed. Check the fender linings and other areas under the hood, along the sides of the engine compartment, for standing water.
Check the trunk or cargo area to make sure that no water leaks through the seals. To test the corrosion resistance of materials and surface coatings, a variety of standardized laboratory-based corrosion testing methods are used, which can be carried out in environmental test chambers. Think about how easy it is to crumble a layer of rust between your fingers, and then imagine that thing trying to protect you and your loved ones during a car accident. Most modern cars are designed with extensive anti-corrosion measures, including transparent paint finishes that protect both the paint and the body panels and galvanized coatings that protect the steel structure of the vehicle body.
Many car wash products include an underbody spray that can help remove salt, dirt, and grime from critical areas that aren't easily seen, such as the chassis, suspension components, and wheel gaps. It's very common for a little rust to rust on a car body, and it's no big deal if it's detected early and repaired. Door panels and tilting panels (the panel that extends below and along the front and back of the car's front and rear doors) are often rusted. It's not uncommon for some components, such as the muffler and exhaust system, to be rusted, and that's not necessarily a reason not to buy the car.