Well, that person would be an asshole. I guess the folks that participate in my contests trust that I am not. Also, a contest like this would be quite hard to rig due to fact that the winners are determined by the score of a game played after the numbers for the boxes were picked.
I get it though, using random.org exclusively on a regular raffle would be sus, which is why I use an rng in discord where anyone that wants to see, can.