“Facial attractiveness influences impressions of honesty.” (Bull, 1979; Berry & McArthur, 1986)
Bond et al. found that people who were judged to have an honest facial appearance (which significantly correlated with attractiveness) were less likely to agree to deceive others. This has Bond et al. conclude that there may be an element of truth that less attractive people are more likely to lie (Bond, Berry & Omar, 1994). Zebrowitz, Voinescu & Collins (1996) also warned (although didn’t directly test) that people’s judgements of honesty may be biased by the attractiveness of whom they’re judging.
Another study by Aune, Levine, Ching & Yoshimoto (1993) found that the opinion of credibility regarding a video recording of a woman (made up, nice hair and clothing) significantly influenced male students opinions, however had no affect on female students (compared to a control where the same woman was plain looking, boring clothes etc).
Finally, Bull & Vine (2003) showed 12 video clips (6 male, 6 female) where participants rated each for attractiveness and honesty. As expected, faces rated as attractive were also rated as more trustworthy.