Check out the used car history records. Most accidents are reported and the used car history report may show you that the used car you were about to acquire had been damaged in a serious accident before.
Thoroughly inspect a used car for signs of previous accidents or corrosion yourself. Is it difficult to spot signs of previous accidents? It's hard, but if you know what to look for, you might be able to catch some telltale signs.
Check how body panels fit together. See how different body panels fit together. For example, the doors, when closed should be perfectly flush with other panels. The same for the hood, trunk lid and other panels.
Beware of mismatched colors and alteration in paint texture. Concentrate on the quality of the paint. A fresh paint may have a different texture, or signs of a body repair could be apparent under the paint.
Look for paint overspray. At the factory, the new car body is painted before anything is installed on it. This means that any plastic trim or wiring should not show any indications of paint.
Have the used car properly checked by a experienced mechanic or used car inspector.