Since photography is a form of art, different people may look at it in different ways. This means that there will be cases where the customers are not happy with what you have done.
In this cases, you may suffer from serious stresses if the customers are criticizing you. After all, a photo can be very important to the customers and you have ruined it.
Therefore, you will need to be having a strong confidence as well as high level of skills in order to cope with that. You just cannot fall into a collapse of hopes just when customers are criticizing you.