It's funny you bring this up. When I sold an iPhone along with an iPad to GameStop during their promotion I realized on the drive home I never reset anything. I knew not to do so in advance because they need to get information off of the iDevice and promised myself I'd then do so when the transaction was complete.
Plain forgot.
I'm sure they're used to this and wiped the devices themselves, but still- best to remember and do so at the time!