New puppy..need some advice!!

I think the lady at the pet store was crazy to be honest.  This behavior "could" be bad, but its a puppy, hes not trying to disobey you or be bad, hes playing, you just need to calmly teach him whats right and wrong.  I wouldnt worry about her, she may have never owned a young puppy.  I think hes acting normal for a puppy. 
 
Bailey did that go for the face thing, even showed her little teeth, it thought it was so cute but I had to be on guard and I just said no and handed her a toy.  She will still do it when she gets riled up but the other day I just sat there (expecting to get it) just to see if she had learned... and sure enough she stopped right in front of my face (didnt do anything - just being silly).  And I do expect that to stop totally as she grows up.  They are by no means bad dogs for playing or even getting out of hand sometimes - they are puppies!... you just have to teach where the lines are drawn.  Sorry that lady made you feel bad.