Its a bit extreme, coz i too have asked the same questions to a pest controller, and their answer was:-
To put mosquito nets on the windows, and have mosquito net doors, which you can make yourself. I know these actually work as i had them on the doors when we lived in Cyprus.
However somebody also suggested that there are some flowers you can stick onto the windows or doors, and apparently once a fly comes in, it dies automatically. I am still looking for these flowers, people have mentioned Fabreeze catalogue? or something like that, or D.I.Y. stores.