I agree that it is unusual.
How do they make money? Does anyone know? I would like to understand better their business model
It's pretty simple really. They basically substituted bonuses which are usually given by many crypto gambling sites with this zero percent house edge model on their originals only upto a certain amount after which 0.1% house edge applies.
They make money primarily through their other high house edge games and through the vig in their sports betting section.
tbh, this is really genius, the 0% house edge is like a loss leader, they use it to get players in, then they make their money from slots and sports.
Is there any way to verify that one is playing with 0% house edge until $50k wager is done? Or one is playing with 0.1% house edge after $50k wage.
Yeah, you can verify it easily by using wagering strategies. The house edge is always 0.10% on the in-house games of Duel.com. They give back the 0.10% commission as rakeback until you wager $50k in a day. After that, they won't give you any rakeback. You have to play for a few hours with a decent bankroll to verify that by using a proper wagering strategy.
an easier way (that requires no gambling) would be to just check the payout/win chance. on a simple 2x on dice, the win chance is 49.95, so 49.95 + 49.95 = 99.9, and 100 - 99.9 = 0.1% which is the house edge.