I used to play scratch offs a lot and for the most part I didn’t do too bad overall. My loss rate was about 22%. I don’t do that hardly at all any more but I found there was one store where I experienced much higher loss rates. For a while I chalked it up to a fluke, but then it became aggravating. I stopped going there, but it was bothering me so I just had to know. I went in a few times and bought larger numbers of the same game, and I made sure to ask that he had plenty of those left first. That is when I found that sometimes the series (the cards are numbered) would be broken up.
I don’t know how they do it, but I suspect that certain people have identified a way to locate the jackpot cards, either precisely or within an area. The store owners/venders are in a better position to identify the patterns. I never caught on to what it was though
Years ago Esso (now Exxon) had a “heads or tails” scratch-off promo game. Some young fellow figured out a key to winninmg. IIRC, Esso ended up giving him a cash award and a college scholarship to show them the flaw.