Corruption is still possible, but the real trick to liquid democracy is that every stage is a form of escalation with the potential for correction.
Let's take two scenarios:
1. a vote is being passed "up" and crosses an extremist channel, it'll likely get locked in and come out even more extreme than it started. extremists tend to look up to people who are even more extreme. when this happens, there's a good chance the person who's vote it originally was will be upset with where it ends up
2. a vote is being passed "up" and crosses an intellectual/thoughtful person, it'll likely get locked into the academic/altruist channel and come out with an extreme subject expert. this is the ideal outcome.
Basically, at any point where the vote is being passed up it can hit one of these channels and get locked in. There's massive (and immediate) drawbacks to letting your vote hit an extremist, and massive gains to passing to someone who's more intelligent and thoughtful.
While you're totally right about peoples first vote being super manipulable, each successive pass off has an opportunity for escaping that mind control. And once it does, it'll stay out.