I don't buy used vehicles either, but I'm not using OEM branded oil. Honda, or any mfr. just pays some third party for oil and sticks their name on it. I've never seen OEM oil as good as other options such as Amsoil. As long as Amsoil, Redline, or whatever other oil company meets mfr. stated standards, owners are free to use what they want....and then there's me - the weirdo that turns a vehicle every year, yet maintains it by the book using exclusively OE parts. One could argue that I'm wasting my time and money even on oil changes, but I like to know that the next owner is getting a vehicle that is as close to new as possible. Unfortunately, few others share this mindset which is one of the reasons why I don't buy used vehicles.
Totally agree with you on used vehicles. You don't know how it was driven, how the motor was broke in, etc.