This frame had been damaged by tightening the seat clamp bolt too tightly. Repaired like this.
Before
After
The manufacturer doesn't want you to know how to do this.
Occasionally, the thread in a crank becomes damaged. The repair method is to enlarge the pedal hole and tap a new, larger, thread in it. A thin steel bush is then screwed and thread-locked in place, creating a thread that is stronger than the original.