The Bellaggio dealers scramble the deck before putting the deck into the shuffle machine. Is that common in Las Vegas?

The Casino de Montreal in Canada has their dealers riffle the deck before placing it in the shuffle machine.

Any thoughts on why the casinos have their dealers do this?

to appease the superstitious nature of their players would be the only reason I could come up with.

Maybe to look quickly for boxed (upside-down) cards?

Both of the above.

I've worked in rooms that required it, and rooms that forbid it.

I could be wrong, but I don't think the dealers at Bellagio are required to scramble. What you're probably witnessing is the dealer fulfilling a request by a superstitious regular from whom the dealer has come to expect a request. It is often a very quick motion with the hands by the regular that the dealer might recognize while you miss it.

A riffle makes no sense if it's headed for the shuffler, but I prefer when they quickly scramble the cards for 5 secs or so just to make sure all cards are face down.

When the Deckmates were first installed in one of the rooms I play regularly, the dealers were ordered to do a scramble and one riffle first before putting the decks in. That's, like, 50% of the entire shuffle effort. Why bother with the Deckmates? They gave up on that pretty quickly. I can't think of anyplace I play that as a matter of policy requires anything beyond "stick the deck in the machine with all the cards face down". Far as I know they will all allow a scramble if a player asks for it. And sometimes dealers will notice the Deckmate is not quite ready with the new deck and to stall while waiting so they don't have to hand shuffle they'll do a scramble, or one half-hearted riffle--then the light turns green and they grab the deck from the contraption.

In a 10 handed NLHE game, there are 28 cards used and 24 in the stub. Automatic shufflers shuffle 7 times. Let's assume that there is a card on the bottom of the deck when it is put in the machine and the shuffle is perfect.

Shuffle 1: 50% chance it moves to slot 51.
Shuffle 2: 50% chance it moves to slot 48.
Shuffle 3: 50% chance it moves to slot 44.
Shuffle 4: 50% chance it moves to slot 36.
Shuffle 5: 50% chance it moves to slot 20.
Shuffle 6: 50% chance it moves to slot 12
Shuffle 7: 50% chance it moves to slot 6.

Therefore without intervention, it is impossible for an automatic shuffling machine to take a bottom card put in the machine and make it possible for the SB or BB to receive it even with a cut. Sure it isn't likely. But if you see the ace of spades go in the machine on the bottom and the SB is betting hard when you have a K high spade flush, it could win you some money.

What piece of garbage shufflers do they use in your casino?

This is not how the shufflemaster deckmates work. They do not riflle the cards as a dealer does. Instead they operate with elevators and grippers that move cards from one location to in the unshuffled deck to a specific location in the new deck.

First a random pattern is selected. That pattern detrenmines that the card in the 6th spot in the unshuffled deck will be in spot number 29 in the new deck and moves it accordingly.

If you wanted to simulate a shufflemaster shuffle you could do something like this. Use a random number generator to select a number 1-52, count down from the top of the deck that number of cards (1 being the top card 52 being the bottom card) that card gets moved to be the bottom card of the new deck.

Now randomly select a number 1-51 count down and move that card to the new deck ....


repeat.....until all cads have been moved from unshuffled deck to shuffled deck.