Ask who will actually treat you
At many clinics, especially chains, a different dentist sees you each visit and no single doctor owns your case. Ask directly: "Who does the treatment, and will I see the same doctor next time?" Also ask about qualifications: a BDS is a general dentist; an MDS is a specialist with 3 extra years of training in one field.
Green flag: A named doctor with a named specialisation who treats you personally, visit after visit.
Red flag: Vague answers like "our doctors are all excellent" without a name.