Throughout the series Hawkins was shown using his cards to predict the future outcomes.
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His cards are shows him the probability of success/submission/escape/defeat/death etc. And itts not like one time event. It was shown multiple instances by now
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So I doubt its a scam. Either his cards have some sorta DF ability or he has the type of observation haki where he can predict future to a certain extent.
If I am not wrong Hawkins was defeated by Law before Kaido and BM entered into an alliance. So he must have read something about Luffy, Law, Kid n Killer. This will further explain how he was so sure that he stood no chance against Kid n Killer but has a 92% chance of beating killer if he fights with him alone.
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Now I am not saying he choose the wrong side as anyone will obviously choose Yonkos over Supernovas but in this instance I felt if he saw outcomes like Kid/Luffy/ Law will surive this raid then he should have been neutral rather than attacking head on when he knew he cant beat Kid n Killer at the same time.