How does one make sure that one is not taking the "black taxi"? Are there letters or numbers on license plates whereby one can tell the difference between the 3?

I understand that "didi" is the local Chinese version of "uber" now that the latter left China.

How does didi compare with official taxis?

How does one hail a "didi" driver - similar to an "uber" driver? Is there a English language app for "didi".

Presumably none of the 3 transportation options drivers accept credit cards? So if we do not have Chinese currency on hand, we would be in trouble?