though if you think that the twitter contests main goal is to attract engagement (farm) then the bots aren't such a big deal, unless they start undermine credibility on the company too much
Partially they can check Twitter farm accounts and verify their quality by audit scores. These sites are not perfect but a company can use it as part of their toolkit to reject low quality accounts and increase effects from their marketing campaigns.
https://twitteraudit.com/https://www.followeraudit.com/Duelbits doesn't need to do anything complicated to determine the winner or reduce twitter users whose accounts are fake in following their promotions because the initial intention of promotions like giveway that duelbits does on their social media accounts is to interact with their users, if so many things are done by duelbits it's just to reduce unwanted things it will take time and also additional labor to make their expenses increase, we just have to act normal if we can get a giveaway then thanks if not it's not a problem at all, because as I said before their giveaway is only for interact with followers from social media accounts so that their casino looks active.