Advice on buying used car from dealership

Hello.
I am looking to buy my first car and am searching for a used Ford Fiesta.

Some branches of the Trust Ford dealership (previously Dagenham Motors) seem to occasionally have cars within the specs and budget that I would be looking for.

Does anyone have any experience of buying a used car from them? I would most probably buy from the Epsom or Kingston branches / or alternatively from the Stamford Hill or Edgeware branches. A few random reviews that I have seen online for this dealership (various branches) weren’t reassuring…

Is it advisable for me to get an independent vehicle inspection of the car I am interested in before buying from them / any other dealership (I would ideally like to do so for my own peace of mind) and if so, how does it work? Will I need to pay a deposit and fill the order form for the vehicle before arranging the vehicle inspection?

Any advice most appreciated.

Cheers