Require them to use wording such as "compare prices on Widgets", "find Widgets", etc.
When I talk to non-techies about Adwords, this is their biggest complaint. They are looking for a widget store, but they waste their time going to price comparison sites or search sites.
It isn't easy to mentally filter these out. Experienced users eventually learn the names of the chief offenders, but it takes some time, and it's still damn annoying.