Is anything wrong with hiring TA as a private tutor? I'm an undergraduate student and recently I've been trying to find a private tutor to help me further expand my knowledge (outside of a scope of my courses). I've discovered one of the TAs advertises themselves as a private tutor. Would it be ethically wrong to hire them? Are there any potential issues/conflicts of interests? 

As far as I know there is nothing strictly forbidding it in the university codes and I would love hiring them - I'm quite picky when it comes to the teaching style and in case of the TA in question I already know it'd be a great fit.
As a lecturer, I would feel that my TA possibly has a conflict of interests if they are also working as a tutor for one of my students. Among other things, TAs are often asked to solve through the final exam, to check correctness. So even if they are not involved with marking, they have access to confidential materials, and they can inadvertently leak some of this knowledge to the student they tutor.