I am of the opinion that there are only a few diferences between them.
1. For instance while an armed robber uses weapons, a mechanic uses tools
2. While an armed robber uses force , a mechanic does not
3. While an armed robbers experience can cause emotional and psychological problems, an experience with a mechanic   
    can ameliorate ur car's condition or excerbate it.
But in the final analysis they all extort money from you (except a good mechanic).