Guessing they mean the fairly common (around me) practice of a cab driver loaning their car to a friend or relative who may not have the correct licenses or carry the correct insurance.
Getting robbed, kidnapped, raped, killed, etc. - I personally had a "ghost" cabbie try to swipe my credit card data using a card swipper, demand to take me to an ATM, etc. - lucky, nothing "bad" happened; after the fact, called in his ID number and it wasn't real. This is a bigger issues in some areas, Uber first introduced a panic button in countries were cabbie attacks were a larger issue, but believe they're even adding it to some cities in the US now.
