I think triplebyte's commission is 25% of first year salary, but that doesn't mean the people behind triplebyte are solely motivated by larger commissions.
If one wanted to speculate about bias, I think it could go either way. It's similar to the real estate agent problem: while at first glance TripleByte is incentivized to get their candidate the highest possible salary to maximize that commission, they also get no commission if the candidate doesn't accept any offers or the offers get withdrawn (presumably? I can't see how else it could work), so like a real estate agent, they want to cycle people through as fast as possible and focus on recruiting as many people as possible rather than optimizing each person's offers. The former is pro-employee but the latter is pro-company. It's not obvious to me how this would work out on net.