What is making you feel useless ??
The tricks that your clients pull that undermine your confidence?
OR
The fact that you yourself are not happy with your work?
Look at the whole picture. If it is only a few , out of many, who seem to have the problems then this is normal.
Are you keeping most of your clients and still building a base or are they coming and going at a fast pace.
Not keeping your cients and being inconsistent with the end result of your work would mean that you havve work to do to increase your skills. BUT don't let a few odd complaints get you down ... women are women, and the public are the public! There are all kinds and sometimes it is not easy. Take the rough with the smooth ... it is part of everyday in the life of a nail technician.