It wasn’t McDonald’s themselves that were scamming, it’s more like the trusted 3rd party they engaged to run the promotion had a bad actor that used his position to fix the game.
He began stealing winning game pieces after a supplier mistakenly provided him a sheet of the anti-tamper seals needed to securely conduct the legitimate transfer of winning pieces. Jacobson first offered the game pieces to friends and family but eventually began selling them to Gennaro “Jerry” Colombo of the Colombo crime family, whom he had met by chance at the Atlanta airport.[11] Colombo would then recruit people to act as contest winners in exchange for half of the winnings.[9][10]
It wasn’t McDonald’s themselves that were scamming, it’s more like the trusted 3rd party they engaged to run the promotion had a bad actor that used his position to fix the game.
And that’s just the start.
https://en.wikipedia.org/wiki/McDonald's_Monopoly