In one daring study (Mace 1972), psychologists persuaded 440 young men and women to shoplift items from ten large stores in a major city. Clerks were less likely to spot shoplifters who were well-groomed and neatly dressed than to catch those with long, stringy hair and sloppily groomed. Presumably, clerks are less likely to suspect good-looking customers of shoplifting and are thus less likely to be watching their every move.

(c) http://www2.hu-berlin.de/sexology/BIB/HATF2.htm