The pipe leading into the front of the cat on my Murano rusted out near the flange. A new cat was $1200 plus install. I bought an exhaust coupling from Canadian Tire for $10 and welded it in with my crappy flux core box. I was happy to save the money, but I feel bad for people who are stuck paying the big bucks for repairs. There's lots of young families where a $1200 plus, repair is incredibly painful.
Another time, I ruined the ABS sensors getting the front wheel bearings out. A new set of sensors was $400. I bought a set from Ebay for $30 delivered.
Something is not right about all of this.