I am very new to this game, so take my comments with a pinch of salt if you like but I have found delight to be contageous, if that makes sense ,
Whenever the customer has caught my eye, all of them have sneaked a peak so far while i am working I say , i really can't believe how well this is coming up well beyond my own expectations or similar I say again at the end also before they get a word in, I think as with all things we want to be happy.
If you tell them they should be happy enough times they will be.
Perhaps I am full of it and have just been lucky so far. ask me again in six months.