Overcoming Bias has an entry on girls and guys, apparently (according to their cited paper) if a girl is less than 90% correct ascertaining guys' intentions with her, she should default to the "guys are on the make" preconception as she will do better.
The problem is that we humans have a hard time determining why we believe certain propositions, due partly to self-deception and partly to our brain feeling like one composite entity (as opposed to a peanut gallery of voices, where we'd be able to identify the moron and not ever listen to their ideas). So, even if you know something to be true, you may not be able to follow it without a large mental effort.
As a practical matter for girls and guys, no one knows their ability to judge other people's intentions unless they've been in a judging situation involving themselves (watching other is not the same as watching yourself). Since girls can't a priori establish the quality of their judgement, they should initially be wary.
Thanks for the pointer from the MaslowsHierarchyApplied comment!