Please tell your friend that a wood deck should clear the ground by at least 12-inches. Yes, treated lumber can be used in contact with dirt, but this would be planned obsolescence. In your friend's case it would probably be most wise to use concrete or stone instead. This would eliminate the high risk of rot and structural pest infestation associated with wood on grade. Also, it is always wise for the top of the deck to be a few inches lower than the interior floor. This helps to prevent water from flooding ? and then damaging ? interior floors. Especially during heavy winter rains and on those occasions when the deck is being washed down. 7 1/2" minus a few inches of step-down leaves less than 4 1/2" of thickness for the wood deck. Not enough thickness for a sturdy platform let alone concrete piers. And that's all there is to it!