The seams
Check the seams between the different parts of the body work, such as the doors, trunk, bonnet, and bumpers. Depending on the build quality, all the seams are of even width, which means that all the body panels are placed straight. The picture below shows the seams around both the left and right rear light units.
You can clearly see that the seams are not of equal width around each unit, however, when you compare the width between the left and right unit, they are all equal. Though the overall quality is not world class, this car has most definitely not been involved in a crash. Symmetry is an important guide line during this check.
Suspicion is in place when one of the seams, for example between the trunk and the rear bumper, is significantly wider on the left side than on the right side. This is a clue for a possible head-end collision in the past.
When the repairs are done badly, the effect is that the new or reconditioned parts cannot be placed back neatly. When body parts are not properly mounted, there is room for leakage. Moisture will penetrate the interior and causes mold and rust. Or worse, interference in the electrical system. These problems often reveal themselves over time when the guarantee has expired.