u talkin about the car warranty or deck warranty? If its the car warranty, no matter who messes with it, it'll void the warranty on the audio components. As far as the deck goes, it really shouldnt matter who puts it in... I install all my own stuff and I never have a problem if I need warranty work (which is very rare), but it helps when you know someone there, they wont give you a hassle.

But if the install is free, then i'll shut up now.