While this is true I've also found something a little counter intuitive. If you dress and look like a schlep but what comes out of your mouth sounds intelligent, fast paced and impressive (note I said "sounds") then the contrast between what the person thinks you are and what you sound like can actually be an advantage in many cases. Same thing happens when people stumble on the hole in the wall restaurant that has "great food you have to try this place". While the food might be great many times the contrast also helps.