If I'm a trader in the highly volatile Celery Stalk market, and I sign a contract with a restaurant that I'll sell them celery at a 5% markup over what I'm paying, and I actually take 7%, that's not "free trade", it's fraud.
Now I don't know exactly what the details of Uber's pricing calculations are. So maybe it's not quite like celery skimming. But it sounds close enough, and is probably worth a law suit to find out.