When a man with a swarthy complexion and a huge beard wearing faded camo gear shows up at your border and shuffles through a selection of passports before deciding which one to try, then hands you one that looks nothing like him, you can be a little suspicious ;-)

Then again at another FSR border I was extremely drunk and insisting to the guard that despite what my passport says I was in fact Dutch and they just rolled their eyes and waved me through... I later bought a passport in that same country.