for number 3, he is a knight, he can't just do anything he want out of his own will, there's rules to follows.
For number 2, she could just ran off with the initial money. she'll be out of town alrdy while mc is fighting the small fries, then call out to the boss to do his data collecting and power show, how many people he has to beat? and surely it's not in a row, girl has a lot of time to bail.
For number 1, it is the most possible way but then, he gave her his money, himself. people saw the girl being given a bag (of money), but nobody heard anything about, and there was no hint of evidence it's his money for betting on himself, just verbal promises. The girl can avoid being accused of stealing but can't avoid being taken care of in some ways by him tho.
And lastly, you guys are way too serious about this.
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He himself said that she's an idiot and overly honest and he wants someone easy to handle to do small things, it's part of the plot.