We have never heard of this happening at any of the reputable legal online casinos we recommend and play at ourselves. However, these sites all have a zero-tolerance policy when it comes to cheating, and you can be sure that any dealer or croupier caught cheating would be immediately terminated from their position, with all affected players being refunded their losses. If, somehow, a dealer were found to be in cahoots with a player, that player would also be banned for life, with all their winnings – and their entire account balance – being forfeited to the site in order to help make victimized players whole.