I've been to places with almost 5* reviews ( only 4 of the 150ppl reviewing weren't that happy at one place).. I don't think it gives you the full picture in some cases. Yes it was a nice place, but I don't think it was amazing tbh, subsequently I no longer go.. after my dentist left, the replacement didn't seem to know how to help me, then came 2 expensive consultations & x-rays with no treatment (which is what I was getting on the nhs, only cheaper!) I decided to go elsewhere.
I was also asked to leave a positive review on my very first appointment which I didn't do, it's not long enough to make a proper decision imo. Maybe most of the others decided it was great at the first appointment, who knows.
The place I go to now is more expensive but better equipped so it's ok. I also found them from this site in the recommendations.. I prefer this place. It's also near 5*
There was another place (probably on a par with the current private dentist cost wise), also 5*, but he didn't listen and had his own agenda.. it's probably a great place for whitening/Invisalign/veneers etc.. I just wanted to be pain free. I never went back after the initial consultation..
Point being I don't think there's anything to lose by going to see what its like and I wouldn't worry too much about reviews, it's whether you're comfortable and get on with the dentist that matters, obviously cost is a factor too. Having not so great teeth gets expensive (I speak from experience!). Presumably your sister is happy there and has good experiences, I'd trust that.
I do remember my grandpa recommending his dentist, so I booked in the same place. After I came out of my 1.5hr appointment with white knuckles and 7 fillings he said "oh, that's not my dentist". Wonderful lol.
Just remember you've done this before and been ok, you can do it.. you can also leave if you're not comfortable too
. Good luck, I hope it works out well for you