There was a technique called "spooking" back in the day which is near impossible to do now since 99.9% of the casinos have readers. Although you can still get a glimpse of the card (via a 2nd person "spotter" opposite at a certain angle) as the dealer is sliding it down to the felt and signal you what it is via some manner. This is illegal. Anyway, since hold-carding relies on human error... it's not illegal. I employ this technique when the opportunity presents itself (sloppy dealer.) Now... if a dealer is showing you his hole card to solicit tips... this is highly illegal and considered cheating. I had one elderly woman (not hold card reading but related in a way...) dealer snapping up (flicking a corner up with her left thumb) the next card out of shoe at me (I was on third base) which definitely influenced my decision! Was she doing this intentionally or just a habit do to ADHD? I'll never know. Then there's card sequencing (ace sequencing), shuffle tracking, back counting... which you can also employ on some games.