Yes. They should be qualified and a member of a respected therapy organisation, to ensure a professional service and an ethical code of conduct.
Experience counts for a lot in therapy. Like all professions, the better therapists will have been practising for many years. They will also have regular training to keep up to date with improving techniques and scientific evidence
A good knowledge of psychology is key. Anyone can be taught how to hypnotise, only those with deeper knowledge will know how, when and what to do to help you reach your goals