It's an interesting question and very much something I spent a lot of time thinking about - neither myself nor my DH are especially 'academic' (I also didn't grow up in the UK so my understanding of the British school system is zero!) and also neither of us had a tutor growing up, so when my eldest was struggling at school and we wanted her to sit a couple of the local 11+ entrance exams, I didn't really know where to start.
My idea of a 'tutor' was someone like a former or current teacher and so I steamed ahead and looked on our local facebook page, and also tried quite a few popular tutor matching sites (you'll see them mentioned on here often!).
It was AWFUL.
We tried two people recommended via Facebook, both former teachers with great qualifications who now tutored full time.
On paper, great. In practice, horrendous.
One of them had awful coffee breath, bad BO and had no idea how to speak to children. I had to air the room out after he'd left (he only came twice!). The other was a woman who'd been quite senior at one of the local 11+ schools, again on paper looked great but in real life seemed constantly flustered and bewildered trying to teach my (very easy-going!) daughter. We then tried a few of the online sites but again, a real mixed bag. I realised too late that just because someone has certain qualifications, actually being able to teach someone, in particular a fairly young child 1-2-1, is a very rare and specific skillset.
Overall we spent close to £750 whilst searching for someone and I was going to give up on the whole thing.
In the end, spoke (vented!) to a mum friend who recommended the company they use and we've been with them ever since. We use them for my daughter, who has just passed an extremely competitive 11+ exam, and also for my son who is in Year 3 for Maths and English/creative writing. They are online, which works a lot lot better for us personally, and the tutors are just really really nice, enthusiastic, friendly people from all different backgrounds. One of my daughter's tutors is at Uni abroad, another has just finished his degree so is tutoring whilst he looks for a grad job. Both kids have genuinely thrived and come on a lot academically just because they really enjoy and look forward to the sessions.
I am happy to share their website via DM - they're a very large and well known company who I've seen recommended a couple of times on here, but they get very good results so get very booked up in some cases months in advance for certain exams.