I don't know the inner workings of casinos in the modern day, but back then we had a lot of ways to deal with cheating. I'm sure there were pros that we never noticed, but the people who read how to count cards and decided to try it out were easy to spot and deal with. I remember one time the pit boss telling me over my shoulder "that's enough, bring it in" and I said "I'm trying!" because I actually was. I had dumped most of my tray of chips (not all that much on a $25 table) and it was very obvious we had 2 people at the table working on the rookie dealer.
He pushed me out for my twenty minute break twenty minutes early and when I came back the tray was full and the players were surly. I commented "what happened to all your chips?" and the guy on third base stood up, pointed to the dealer that replaced me, and said "that bitch took it all". Cue security and the table cleared out just about instantly.
A few of the things we could do to change things up on a blackjack table:
- burn extra cards
- change the shuffle
- new deck of cards
- prematurely end a hand
- encourage non-standard play from the other players
- encourage a player to walk away
When I ran into the players I mentioned above, I only knew about burning extra cards. You pick up other ways from other dealers who've been around longer and want you to pull your weight by bringing in better tips.
For roulette, there were just the two ways (changing the ball, stop and start the wheel), but it was pretty rare for me to deal that game, so who knows.
Starts at 3 minutes:
Still, it's discouraged. The casinos would much rather a weekend tourist walk away with a day of winnings than a pro. Tourists tell their friends and inspire them to visit.
Apparantly they did some consulting to the gambling industry afterwards and that is the origin of the diamond-shaped obstacles which add more unpredictability to the ball.
Though given the Real Hustle video posted by another commenter, the same idea still works today, but the calculations involved must be more significantly complex to compensate.