Airdrops on crypto is still can’t solve this no matter how hard they requirements since cheater will always find a way to cheat and take advantage on free money. Ignoring the giveaway is one way to let our mind calm down or just participate but don't expect to win.
I am sure that as a big gambling site, Duelbits has very strong tools to detect cheat on their website. If they can not detect cheating activities, their business will run out of money soon because cheaters will not stop if they can cheat and get money.
Giveaways are good promotion to gain new users or force users to bet more actively. You can simply use airdrop, giveaway coins or free spins and bet to have fun. You can make deposit and bet, it is your responsibility to bet responsible and protect your capital. Gambling with free spin or own money, don't hope that you will get rich by a bet or some bets. It is unrealistic and I only consider gambling like gaming, play for fun and bet for fun.