In practice it's usually the tenants picking the rent split, not the landlord. Two friends move in, they agree that they'll split the rent roughly equally, but maybe the bigger room is worth an extra $50 or something. Often they'll just split the rent equally despite an obvious difference in objective quality between the rooms. This is because when it comes to family and friends, we often behave in anti-capitalist ways. This is why the idea of capitalism seems "cold" and "uncaring", because when it comes to those close to us we don't act strictly capitalistically.
Sure they decide among themselves what the split is. But I mean, if the richer person is willing to pay $750 for the better room and the poorer person is willing to pay up to $500 for either room, the best move for the landlord is to raise the rent overall!
