Auto body filler, also known as Bondo, is a common product used in auto body repair to fill in small imperfections. However, there are some common problems that can arise when using body filler. One issue is over-grinding the metal on thin metals, which can weaken the metal. Another issue is accidentally getting filler in cracks, gaps, holes, or other areas where it is not needed, leading to extra time being spent sanding and cleaning it out during the shading process. It is important to be careful and precise when using body filler to avoid these issues.