Question about US Business Trip

Hi,
I am traveling to the US from Vancouver for 2 nights, 3 days to visit a store that my company operates out of McChord Air Force Base.

I was told by 2 border guards that since I am not being paid by an American company, that it is not a problem. I was just curious if I require any other documentation before I attempt to cross the border (other then my itinerary and passport)?

Thanks

That should be sufficient.