might be a silly question, but how do i accuse the immigrants of lying if their purpose of arrival is different then the one written on the entry permit?
for example they say they are just passing through but the paper states that they are visiting a friend.

I had one who said "I'm staying forever" and then changed it to a week! ;)

Well maybe not "insta-detain" as such (depends on the country I guess), but yes definitely grilled with multiple follow-up questions - who exactly you're visiting, where are you staying, are they related or friends, etc. If they stumbled on the follow-up questions, then it could get more interesting... At the very least they'd have their luggage closely inspected, looking for evidence of a longer stay, or other dodgy things (e.g. undeclared large wad of cash).

To be honest the first few times I had this happen to me, I checked them VERY carefully, thinking that there MUST be something wrong somewhere. Would have liked more follow-up questions, but still a great game.

Would also have liked more people to offer me bribes (hey I need to pay for rent every day!). Most of them still try to deny they have contraband even after the strip search: "You can see that?". Kind of funny though. Gotta love Jorge though: "Is drugs!". He gets points for honesty. :)

That's actually a great idea. I hope a sequel or a major patch / DLC adds this gameplay element. Hehe, yes I did that too. If a person comes off suspicious the moment he walks in, there must be something wrong with their documents: why else would they be so nervous as to mix "a week" and "forever" like that... But often the other information checked out just fine. Maybe it was because they were so afraid that if they'd get a red stamp, something terrible would surely happen to them in their own country.

I was actually saying that was how it seems to work in the real world - at least on "Border Security" (one of those COPS-style shows where they film dodgy people trying one over on Australia's customs people); however I wouldn't mind having that in a DLC - this game is really good, but it's a bit short on content - it's begging for a DLC or at least mods.

Although for the setting, they could come in their cars in addition to coming on foot. Then they could have car-bombs, car searches (for bombs, massive drug caches), possibly impounding the cars for further analysis by some off-screen team... Yeah possibly. Also Arstotzka's border security does look a little bit threatening as well, so would understand mixups between a few months and a few weeks, or forgetting they're here for work. Saying they're here for work when they're not though - that definitely set off red flags!