Sorry if this question was rhetorical.
Answer: Nothing
What do you propose?
Do psychometric surveys exist to identify risk individuals?
Should this be Uber's responsibility or the taxi directorate's?
Is there a problem that actually needs to be solved here?
In one of your posts yesterday, there was an article about all-female ride-sharing, which I don't have a problem with, but I think that there is no absolute way to prevent crime.
A certain number of assults will take place in ride-sharing cars, just as P platers will continue to kill themselves.
Mexico City has female only train carriages, which boostes ridership and made life easier for women. Great!
But what is the problem, proposed solution and desires outcome here?
What you seem to be asking of Uber (this time without mention of ethnicity ) is to make sure that its massive independent workforce are unlikely to ever commit a crime, I just wonder how this is to be accomplished?