Sadly this is becoming the norm, and for most EU countries, and some of them act more third world than you would expect. My experience, and others is that the best is to pre-empt these muppets.
Get certified, in other words official like stamped, copies of all your docs. This includes a lawyer drafted, officaially stamped, gold plated, looking letter with the owners declaration that this is his aircraft for his company and will carry these persons. Make copies of all put in a give away nice looking package with a multi language explanation on front of what it is.
When said baboons arrive pretend not understand a word they utter and throw said folder there ways, saying gift for you.
It seems to work, but all depends what side of the cubicle said official woke up that day. Some of them can be right pricks though and sometimes the thought of revisiting my African ways and slipping the ole waxy note between the fingers.
Usually a coke helps, but these days it constitutes bribery anyway, so might as well go the whole hog.
All I know is that it is going to get more difficult, and these guys are looking to fill there coffers with fines and impoundings. Be careful out there as it is going to get more interesting.