All right let me see if I can break this down because it seems like a lot of people are confused. (Most of my supplemental info is from the WN so there's probably some discrepancies on some of the LN points)
First the terms of the bet:
If Rakan wins Maomao will become his daughter. his reason for saying this is mostly because Maomao refuses to even acknowledge his existence (She partially blames him for her mothers death. in the WN she mostly refers to him as the weirdo tactician and pretty much never directly acknowledges their relationship up to this point) and despite that he still cares for her.
If Maomao wins he will "redeem a a Courtesan from Rokushokan". Maomao is being deliberately misleading here by omitting the name and implying that the Courtesan in question is her mother (who's dead at this point in the WN but Rakan doesn't know that having pretty much no contact with her). I believe the actual courtesan she's intending to set up Pai Rin up with Rihaku (see the beginning of ch 36.1) and to make Rakan pay for it.
Rakan has no reason to back out of the match because from his point of view its a win win (getting his daughter vs an excuse to redeem the woman he loved)
Next setting up the rules of the match:
when talking about the medicine/poison Maomao is actually referring to the alcohol (from the LN "alcohol is the mother of all medicne" after she wins), she holds up the packet of salt/sugar when she says that to deliberately mislead Rakan again into thinking that there's actual poison in 3 of the glasses.
the Actual match:
first of all Maomao has absolutely no intention of winning the first 2 matches, thatch why she declined the handicap. For her plan to work she actually needs to lose the first 2 rounds.
when she loses she drinks the entire cup each time. This hasn't come up much in the manga but she's actually a pretty heavy drinker despite her looks/size/age. She's again doing this on purpose to make Rakan think that even though he's a lightweight surely the alcohol can't be that strong if a little girl can knock back 2 cups (he is very wrong).
So now Maomao has him backed into a corner were he thinks his options are 1) win and risk killing Maomao (which makes winning pointless), 2) leave and miss out on the supposed win/win I mention earlier or 3) lose up to 2 times on purpose to makes sure he gets at least 1 cup of "poison" to make sure she's safe and hope he can handle up to 2 sips of supposedly weak alcohol (actually extremely strong alcohol).
So he hedges his bets and picks his only supposed path to victory option 3 and gets immediately wasted because of the salt and the fact that he's a super lightweight.
And that's why Maomao is such a giga mind, she had him beat the second he agreed to her terms.
Tysm
