ANSWER:

This is permissible but you shouldn’t assist them in choosing what is beautiful for them and suites their faces. Let them do that by themselves. 

QUESTION: Is it permissible to work at a opticians where the job could involve speaking to female customers/colleagues aswell as assisting and conducting eye tests on females, in addition where the job could involve helping female customers choose glasses that are ‘designer’ and meant to look nice/fashionable aswell as selling these glasses to them, which could be unavoidable