Be careful! I have seen multiple "ugly american" warnings regarding Americans going to countries like Guatemala and being too assertive. It seems to really agitate Latin Americans who don't share our North American zeal for productivity and speed.
One thought might be to do your best to establish some sort of personal relationship with the Guatemalan stakeholders. If they feel like they are working for you as opposed to the contents of your wallet, you might expect (and feel) better "service."
Andrew