Then he looks at his card, and pushes it out.

With his hand still touching it, he watches the dealer and, if he can see by his face that his card is a good one--and you can generally tell that--he withdraws his hand with four of the sovereigns, leaving only one on the card.

If, on the other hand, he thinks it is a bad one, he leaves the whole five there.

He does the trick cleverly enough; but I am certain that I have, four or five times, seen him do it.
"Keep your eyes on his hand.

You will see that he takes up five sovereigns from the heap before him, and that he has them in his hand when he pushes the card out.