Don't shoot the messanger (or mechanic) or be to quick to call B.S. As almost any shop that works on exhaust systems has gotten bit by some state or federal regulator.
The entire exaust system is covered under EPA (federal) regulations and in certain states is covered under state regulation as well. Since the 90's there are so many regulations on automobile repairs its almost impossible to tell if by turning a wrench if you are breaking the law. Its why I don't own a shop anymore. Seemed that you needed one lawyer for every two grease monkeys you had in the bay just to keep yourself out of trouble.
The laws and consequences for shops has gotten pretty strict. Most shops are blissfully unaware of the mine field for which they play. The issue being that is the regulations are complicated and sometimes confusing. But the general guidance from the industry is that any modification that bypasses a emissions component or modifies its functions is considered "tampering" and whether or not the shop did it, or the shop just touches when doing a repair, they can legally be responsible under the law. But seems everyone has different opinions of what an "emission component" is. Unfortunatley this means that some states will say things like larger pipes are not legal because they reduce back pressure which effects the emissions profile. Depending on the state, the statutes, and the whether the inspector has had his coffee yet they can cite for all sorts of things.
Let pick on Ohio, as that is the one I am most familiar with:
One good example is the customer who wants their truck converted from single to dual exaust. Gets real frustrating when customers get so upset when you can't do something.
Q22 Is it tampering to install a dual exhaust system on a vehicle originallyconverters would, therefore, be considered tampering.
The question 22 from the Ohio FAQ comes directly from the EPA guidance that was released in 1991:
equipped with a single exhaust?
Answer 22. The general rule is that a motor vehicle emission control system (which includes
the exhaust configuration) may not be changed from an U.S. EPA certified configuration without
subjecting the repair shop to liability for violating the state and federal tampering prohibition.
The exhaust system configuration, including the location of the converters, and exhaust pipe
diameter and length, are items specified by the manufacturer because engines and some of the
associated emissions systems are generally affected by the exhaust system back-pressure, which
subsequently affects vehicle emissions. The installation of a dual exhaust system with two
Where its listed as question 7.
The "voiding of warranty" area is questionalbe because of lack of clarity under what conditions a shop becomes legally liable when working on a vehicle with a modified exhaust system. Depending on who you ask, or what EPA document you read, the shop may.....or may not....be required to return the exhaust to stock if they end up touching the modified exhaust system. (Try explaining that one to a customer) So many shops/dealers just refuse to work on engine or emission system with a modified exhaust.