As has been said.
Any betting system, any method being sold, anyway to beat the odds...
If it was to be invented AND was foolproof the owner or inventor ould be quietly using it and making money rather than selling it.
With casino Blackjack, if certain circumstances arise and with careful betting it is possible to move the odds into your favour and it was possible to make money. It's called Card Counting, it was used by the inventor and plenty of money was made, UNTIL the casinos recognised what they were doing, and took legal and illegal action. To use the method effeciently took a team and a computer, the feedback from the computer needed to be hidden but as a Blackjack dealer it was possible to recognise what was happening by the betting patterns. Legally, you upset their system by making a less deep cut of the shoe, then less cards came into play and then less chance to move the odds, also legally the casino could refuse you admittance or reject your bets. Illegaly, some nicely dressed 'gentlemen' would convince you that you did'nt want to play. There were people who could perform this in their heads and without electronic help, but once again the betting pattern would expose what was going on.
At this point selling the system would be a money making option.
There were out and out cheating methods to force a win at the tables, but were generally messy and soon it was obvious to an experienced Dealer and table Inspector what was going on. Driving out to provincial casinos, with less experienced staff worked for short periods of time but...
Casino security was high, CCTV in use, the images and names of characters would be circulated.
Anything involving a third party (an animal) does offer openings, inside knowledge is there but again not usually widely circulate simply because with variable priced, course betting the odds change quickly, so once a 'certain thing' becomes known, money goes on and odds shorten and even a 'certain thing' is not usually certain.
Knowledge of an illegal 'certain thing' will not usually be known and if illegal there will be fall back remedies to organisers and the bookmakers.
There is also the use of information that is in the public domain, but it is having the skill to digest and process in another matter and by no means certain. It is this sort of information that gets sold with much publicity when it come home but little said about failures.