Asking your friend for choosing a dress for you can actually be a disaster. Research has shown that we normally overestimate our friend's knowledge about us. So they are not the best agents when it comes to making choices for us. And the reason for this over estimation is over confidence. This overconfidence is the over confidence about the knowledge about us. Our friends normally have an automated part in their memory that knows all about us and the mind does not bother to reason that automated part, because it is expensive to use the memory. Ultimately the big question is "Does our friend even bother about us ?" Well research has not ventured into that domain, but it can be argued that the "Know it all attitude about a friend" may cause insensitivity.
The impact of this research is more for consumers than marketers. The bottom line: "Never trust a friend in making choices. They are bad agents."