Eating - lack there of

Question
I have a 16 week old lab we just got him from a reputable breeder 2 1/2 weeks ago.  The first three days he was here he would gulp down his meals, after the third day the food the breeder supplied ran out.  We bought the same food (Iams puppy lg breed)but he hasn't eaten the same since.  He was eating 1 1/2C three times a day.  Now we're lucky if he eats 2C a day and that's with bribing him.  We've tried it softened with water, hard, in various bowls, on the floor (he seems to prefer this) and out of our hands (he likes this too) and only feeding him twice a day and jut leaving the food out for 15mins and taking it away until next feeding.  He just sniffs it and walks away.  He is drinking plenty and using the bathroom fine.  He is playful for the am and then sleeps most of the rest of the day.  He hasn't eaten a thing today and it is late afternoon.  I called the vet and they said as long as his energy level is up don't worry too much.  But, he looks gaunt to me and his stomach area is sucking in now.  Do you have any suggestions?  The breeder had none.  

Answer
Over feeding a Lab to where it won't eat is unlikely, but possible.  See this guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx  With a Lab, don't worry until you can actually see the ribs.  Most Labs die a premature death due to overweight.  

The food should be fine, although you can switch to an adult chow any time.  doing so slows growth allowing more time to develop sturdy joints.