[Johnnyvav]

Here's the problem. They will fight you and try to blame anything on any aftermarket product you have as the root of all evil.

Do they have to prove it? It depends, what are you going to drive for the next seven years while the case is caught up in the court system?

You need to stay level headed, appear knowledgeable, and compliment on the service you have received up to this point. This way you can hint at the loss of future business.

Example:
Mr Service Manager, c'mon, do you really think my cat back system could cause my (insert part here) to malfunction? That just doesn't make sense. I have to tell you, I love this car and up until now you guys have treated me really well. In fact my wife's lease is up in a couple of months and we are planning on picking up a (insert dodge/chrysler dealer here) from you guys but if we can't get this fixed to my satisfaction, I just can't bring myself to buy another car here. Can you get this done for me or do I need to speak to someone else?

Oh, you'll take care of it? Great I really appreciate it.