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The draw should be in the form of live from gathering participants until choosing it using random app to make it more transparent.
Just like many other casino that never shows how they draw the giveaway just to make an engagement for there social media.
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Something to think about...

The Casinos do a whole lot just to get engagements on social media. I think its just a way to get the attention of gamers because amongst everyone who comes across the comments, there are people who will be seeing the game brand for the first time and will want to check it out. That logically translates to one more user for the brand.