I'm quite sure you weren't being judged for being ugly, you probably aren't. But, i had a friend who had the same complaint and didn't understand why but to be honest she did honestly look greasy and not very well maintained... I however didn't really have the courage to tell her to work a bit more on her appearance but i'm pretty sure the costumers were right. People don't go that far to complain about something like that if it's really not that bad. You DO represent a company and judging from the complaint, you represent a company that requires a bit of a well maintained appearance, most do. Really.. Except MC donald workers to be honest. I assume your hair was messy and must've looked greasy or something which even kind of disgusts me as a customer too. I don't want someone who looks like they haven't washed their hair in days touch my food either. Or wherever you work at. I'm sorry but most people would be turned off.

No from the sounds of it its because you probably look like a slob. Brush your hair and make it look nice. That will help a lot.