dents 

Processes for repairing dents vary depending on the type and position.

Examples are -

Small dents where the paint is undamaged can often be removed using Paintless Dent Removal (PDR) techniques where the metal is shrunk back using tools mostly from behind. These are often referred to as shopping trolley dents.

Larger dents may require panel beating, pulling out from the front using glue pulling or welded tags or PDR from behind or a combination of all.

In some cases a similar dent on one car can be repaired whilst on another, the panel needs replacing. The yellow MG wing can be repaired but the Audi wing because of its inverted swage line, which is difficult to replicate, is best replaced.

Sometimes it’s obvious the panel needs replacing - last picture.