What causes CV joints to go bad?

[Sk8rdi16@cs.com]

I have had my CV joints replaced twice within a 6 month period.  It was done
by a pretty reputable shop. They gave me lifetime warranty on both.  So my
question is what is the cause of my inner cv joint going bad? The guy said it
was bad motor mounts, then he preceded to rock my car by popping the clutch
about 60 times. Then he said I lowered it wrong.  I have the hypercoil
springs and KYB AGX.  Could it be my motor mounts are bad. If so how do can I
tell? Thanks in advance!

Pat
91 SE-R