Frowning. And make sure he is using stainless decking nails...
http://fasteners.hardwarestore.com/18-67-nails-bulk-specialty/stainless-decking-nails-102303.aspx
What is his method for spacing? There are different schools of thought on that. Not touching, but closer than the thickness of one of the nails is best, IMO... because the space gets larger with time, and if you start too large, you get mosquitos coming up from below unless you screen it in below deck.