This is an effect that I use to practice the Erdnase system of cull shuffling.
Effect: The performer shuffles a deck of cards and then has the spectator shuffle them as well. The performer then takes the deck back and ribbon spreads the deck face up on the table, remarking that the deck is now well shuffled as the spectator can see.
Picking up the deck the performer give the deck another shuffle, overhand shuffling the cards.
Then explaining how card sharps always need to find some good cards for their hand, the performer turns over the top four cards, revealing the Aces.