Do shops still sabotage cars for profit?

A few years back, my wife's grandmother had an older bowtie. It started to stumble badly went pulling off and at certain time. Started and idled good just problem when giving it gas. Took it to a dealership several times. They replaced all the expected items including plugs, wires, points (yes it was that old), etc. but she still had the problem and asked if I could look at it. Well the dealer had replaced everything I could think of but I agreed to look. First thing I did was remove the air breather and while takeing off the wing nut, the carburator shook. The problem all along was the bolts had virbrated loose. She spent a lot of money due to two loose bolts.