How do I know if a dentist is any good?

That's a really difficult question - rather like choosing a car mechanic. You should always check that dentists do continuing education, that they have proper sterilisation procedures in place and that they wear loops (special telescopic glasses). Next, are you comfortable as you can be at the Practice and do you trust the dentist. Ultimately, professional relationships like Doctors and Dentists are always  based on trust, which normally develops over a period of time.  Sorry - that's the best answer we can give you... so beyond that... go with your gut instinct!