There's no real way to be 100% sure of any search volume unless you force your way into the top results and track the views.
The web landscape is full of scrapers, bots and other interesting things that can artificially boost search demand, thus affecting our decision to by EMDs.
I usually value my common sense more than the numbers that the Adwords Tools gives out.
Another tip to keep in mind would probably be Adsense Average CPCs if the sites are going to be MFA.
Its a volume game with EMDs right now, and sometimes you may just get slapped by Google for owning too many EMDs.
I'm starting to convert most of my one-page EMDs to 7 or 8 pages in order for them to conquer the Google "possible ban" threshold.