It can be combined with other complementary therapies such as acupressure, shiatsu, yoga, tai chi, colour therapy, magnetic therapy, meridian therapy, and reiki. The answer is subjective. Surely you don't want someone who had just read a book about it. On the other hand, there are many practitioners who have had seemingly a lot of training but still not be good at it. Something that feels light and rather like a foot massage is pretty bad.
Many people go to reflexologists for stress related problems or injuries.
It helps people to relax before surgery - and also to heal more quickly.