Arbusers

I'm trying to become a professional bettor and, further an extensive research, I came to the conclusion that I need a Singbet account. Understanding that they only provide accounts via agents, I found several, but I am puzzled about the "commissions" charged.

Can anyone explain in simple terms why some offer to provide me with accounts at 50%, and others at 70%, meaning they retain 50% and 30% of my winnings respectively? Note that they are asking me to fund the betting account with the same proportions, so this is not a commission as such - I just fund half and they retain half of my winnings, so effectively the exact same.

I cannot possibly understand why they would do something like this, especially since I was under the impression that they make profits only if I lose.

Thanks!