Don't allow HTML rendering of <a> element where href links to another URL than shown, don't allow any (java)scripts to run, or at least give user a warning that he is about top open a new window into domain XYZ.

This is how I found out quite a few scams (apart from obvious ones with improper wording or visual formatting, but those are on purpose so bad to catch only most unskilled or gullible, ie your grandma)