What part of getting the paper work before they have an opportunity to figure out something is up and alter it is unclear to you?
Oh, I don't know. This was a new vehicle purchase. Every new vehicle I've bought has had the dealer sales people stress at how I ought to get all the service done there because they really know what they are doing. Every vehicle's owner manual states in several places how the authorized dealers know all about MY vehicle and how it will be serviced and repaired exactly as it should, that I should have no worries about a dealer doing it.
Maybe that doesn't happen with GM's? I wouldn't know, haven't bought one since 2000.