I'm the store manager at my place of work, and am in charge of all the hiring. You don't ever want to state that you do not have any flaws. Everybody has flaws, nobody's perfect. If someone told me they do not have any flaws in an interview, that to me would be their first flaw, they are a liar, and will say what they need to to me to get the job, and in the future they will lie to stay out of trouble. I agree with above stated "taking on too much etc." Others might be being self critical, or you could even put it more directly to working at MAC and say u could work on product knowledge. As for strengths, in retail position you want to stress people skills, and sales as strengths. Good luck!