The following description of hole-carding is taken from our book Cheating at Blackjack by Dustin Marks, one of the all-time greatest blackjack cheats, especially considering he cheated from both sides of the table—player and dealer—and was never caught.
There are two main types of hole-carding: “basing” or “first-basing” and “front loading.”
Basing means seeing the dealer’s hole card when he checks under his up-card for a blackjack. Basing was possible when dealers checked for blackjacks by lifting their up-card and checking the hole card, but it’s as good as nonexistent today; virtually all casinos now have hole-card readers that optically check for a blackjack without the dealer having to look at the hole card.
Another hole-card play, “spooking,” was similar to first-basing. For this play, the reader (“spook”) was on the other side of the pit, behind and to the left of the dealer. When the dealer checked for a natural, the hole card was visible from behind. The reader then signaled the Big Player at the table.
Front loading is seeing the dealer’s hole card as he’s tucking it under his up-card during the deal. Front loading yields a stronger edge, since the hole card can be seen every round, as opposed to only when the dealer has a 10 or ace up. New dealing techniques have made it more difficult to find “loaders” (dealers who flash their card), but the tactic is far from obsolete. Additionally, front loading can be used at many of the carny games, such as Three Card Poker and Mississippi Stud.
Some dealers can be read 100% of the time, but most fall well below that. Still, if a dealer is readable only 30% of the time, that’s enough to create a good edge, and it can be coupled with card counting or other advantage techniques.
The strongest of all hole-card dealers is the index dealer, who accidentally shows the hole card in a way that makes it readable from the center of the table. Index dealers are very hard for the bosses to detect. The only way to spot one is to be in front of the table somewhere near the middle and watch very closely. A good index dealer is money in the bank.
I played a lot of hole card in my day. I didn’t always win, but in the long run, it was profitable and safe. Though highly frowned upon by the casinos (and even by many players), hole carding was legal back then, as it is today.