Where is the line between being cheap and dirty looking and being glamourous and classy looking?

Obviously there's the obvious too much make up (ie orange face and mascara caked on etc) is classed as quite trashy and glamourous is dressing very sophisticated and knowing where to stop with the make up... But what if you AREN'T going to a grand ball so wearing a ball gown to look glamourous is out of the question? What if youre just going shopping? How do you still look classy and pretty and very showbiz without being OTT? I'm just wondering what people think because personally, I think no matter how classy you look you will always get at least one girl who calls you trashy!