I believe that being asked for bribes depends a lot on your look and attitude... I've not been travelling everywhere (far from that) : I've been a few times to north africa and central asia. When travelling, I don't really look like the rich westerner : 2 months beard, same shirt for a week, a shower once in a week and so on... In areas with a fair amount of foreigners, I guess I look like a hard job in comparison to other travelers (and I try to be). As a result, I've really rarely been asked for money.
Compare that to a middle-aged swiss couple I met in Kirghizstan : They drive a rental land cruiser (just the two of them in it, a rare sight in the Pamir!), they are clean, they got all the brand new gear and look impressed by every man in a hat they see... If I was to ask for bribes, I'll go straight to them, not for the broke looking bearded dude who smile like a retard.

I doubt my look is my only safe-conduct : I try to be nice to the officers (after all, they are just doing their jobs), shake their hands, never refuse to give a cigarette when asked (even though I quit smoking, I keep a pack for this purpose) and ask them questions about them (If they are from the area, if they like it here, if they know my home country, etc...)

Anyway, I think we can all agree that smiling and playing dumb is the basic here !

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