How experienced is some one at front end if they use Wordpress for every site? Genuine question because I've never used it and usually create my templates and design (not very good but hey I'm not frontend) from scratch.

It varies, wordpress doesn't really restrict the frontend and using prebuilt themes is optional.

I'd question their backend knowledge instead.

@ItsNotMyFault I would only hire them on as frontend. Thanks for the insight.

@dalastTomCruise take a look at what they built, if they created their own themes and they are good and reasonably modern from a technical pov then it should be fine. If they just adapted or re-used other peoples wprk then i would avoid them.