If you are not from West Africa (the Economic Community of West African States), then you will have to present a valid Visa upon entering Nigeria. In general, ECOWAS members ( Benin, Burkina Faso, Cape Verde, Côte d'Ivoire, The Gambia, Ghana, Guinea, Guinea Bissau, Liberia, Mali, Niger, Senegal, Sierra Leone, and Togo) don't need a Visa for a stay of up to 90 days. Customs officials wil generally not disturb West Africans or ask many questions from them, and indeed Sub-Saharan Africans in generals are hardly ever questioned (On a recent trip back to Nigeria, all Nigerians, West Africans and Africans were treated on the same queue, while all others were separated to another queue). However, if you happen to be European or American, then it is very likely that the Customs officials will cross examine you. On a good day, their questions are generally along the lines of:

 "What is your mission in Nigeria?"

"Do you have any concealed drugs on you?"

"Do you have any goods worth more than $5000? If you do, please fill out this form, indicating what these goods are and the reasons you have brought them with you"

Rarely, they could ask you something like this: (This was asked once of a South African man whose passport for some reason indicated that he was a former Private Soldier)"Are you a mercenary supporting any separatist movement in this country?"

Now, if you are Caucasian (this may sound racist) and are travelling without a Nigerian or African with you, you could be taken off to a questioning room and explicit bribes may be demanded from you. Best advice to any Caucasian visiting Nigeria (alone) will be (if possible) to bring only hand luggage and forget about the checked in luggage. This is because Customs Officials could invent excuses to impound your checked in luggage if you refuse to give them bribes. If you only have hand luggage, then this problem, of course, is eliminated. In the event that you have to go with checked-in luggage, then your life will be a lot easier if you do not become belligerent with Customs Officials or anyone dressed in military gear in Nigeria. The Army/Customs Officials are ruthless and basically run the country - do not become belligerent with them, whatever you do - nearly all of them are armed to the teeth and will not hesitate to use any means possible to have their way. You may be searched three or four times (by Customs, by Immigration, by the National Drug Law Enforcement Agency, and very rarely by the Army - in times of heightened Security).

 Oh yeah, one last thing about bribes: If Customs Officials demand bribes of you, you can empty your bags and show them that you have NO/Little money on you (Best keep your money in the middle of a book or in a well-hidden place). Of course you can't do this if you're travelling with large wads of thousands of dollars (as many Europeans/Americans do when visiting Africa for the first time), but if you explain to the Customs Officials that you haven't got any money, they'll be reasonable and let you go. On the other hand, if you walk into Nigeria with large gold chains and diamond earrings and fancy iPods and expensive camcorders and things, be prepared to spend a few more hours being harrassed by Customs Officials.

Now if you have a Nigerian or other African friend with you, this is not likely going to happen. Your best option would be to stick to your friend like glue, especially when the Customs Officials are checking your passport and luggage and things like that: Talk with your friend, and show them that you KNOW someone from Nigeria - they'll likely not bother you if they realize that you have an African friend! 

 If, however, you are European or American without a valid Visa, then the first thing you should do is to get in touch with the US Embassy or respective Embassy in Nigeria. It is imperative that you do this: if you cannot get in touch with the US/European Country's Embassy, then the Nigerian Customs Officials will take you to hell and back. Nigerian Customs Officials are often hard-hearted and have heard horror stories of Americans and Europeans being thrown in jail before being rescued (after spending days in terrible Nigerian jails) by their Embassies. DO NOT leave your country without a VISA!!!

A word to the wise: Nobody likes somebody that looks scared, uneasy, apprehensive or in any other way uncomfortable, particulary Customs Agents of any country.  A smile, a look of pleased be where you have arrived, looking right in the eyes and showing you are co-operative but not a dupe, goes a long way, even in, ye gads, Nigeria!!  In fact, use your friendliness as a contagion rather than your apprehensiveness as a red-flag that signals potential trouble.