Originally Posted by BTM
The exception I take is the "X is connected to Y is connected to Z" game that dealers will try and use (not every dealer does this but some of the stories are pretty bad). Denying service on wheel bearings because of non-rfts or on turbos because of a cat-back exhaust are completely ridiculous. Wasn't there someone who's catalytic converter warranty was denied because they had the valve opening wire unplugged? When BMW themselves sell an exhaust that bypasses the valve?
In many cases I agree with you however. There is a guy on another forum that always bashes his old N54 as having been a piece of junk - which he had modded to the hilt and was getting about 430hp out of, I'm always like, you don't think that had anything to do with your crappy reliability?
Often, that is based on a previous bad experience, ignorance on the dealer's part or a crappy customer.
If a customer goes to the dealer with a car that is scraping the weeds, a catless exhaust and a bunch of bling then the dealer may well start looking for exclusions. If the customer comes in with an attitude as well then he can kiss warranty service goodbye.
A reasonable customer with a few reasonable mods probably won't have issues. It is the "bling mods" that draw attention to the mod and bring little in return - these are cold air intakes, catless exhausts and similar mods that scream "look at me" but bring very little in terms of performance.
Combine that with a service writer who doesn't understand the intricacies of mods and you're in trouble.