We would be lying if we said that no casino has ever tried to cheat players by putting magnets on their tables. However, such techniques were used more often when casino gambling wasn’t as regulated.
Nowadays, if a casino in countries such as Australia, the United States, Macau, or Monaco, were caught with such a table, the parent company would have a nasty lawsuit on their hands. Generally, casinos try to avoid lawsuits, so you won’t find them cheating (that’s what house edge is for.)