I'd be inclined to trust YC that they make their money by picking AirbnBoxen rather than chiseling twenty somethings out of a few thousand bucks. Even if I were cynical regarding their motivations, I would personally take a YC investment as a Good Housekeepng Seal of "will probably not pull sociopathic moves.". My theory: founders only need to exit once and might be tempted to get screwtastic. VCs face no market penalty for screwing employees because a) employees have severe information asymmetry when it comes to deciding who to work for based on investors, b) the Valley practices institutional omertà about speaking ill of fellow investors except over backchannel, and c) a reputation for chiseling out employees doesn't hurt VCs at their main opportunity for market feedback: seeking LP.

By comparison, YC is an early employee-comprehensible brand, and I'd expect anyone contemplating screwage would hear "You are about to chill hiring at several hundred companies in the mafia. Are you sane?! Don't do this. If you insist on doing this, we'll be forced to very publicly disassociate ourselves from your decision. You do not want to be the one ex-mafia guy in the Valley. It is a lonely place."