Be very cautious with Nigerians, alot of them are scammers, atleast online.
In my opinion don't buy from any seller that does not accept paypal or credit cards. Unless they have good recommendations and you've used them several times before and can trust them.
Wire transfers and money orders offer you NO protection. Scammers love these payment methods.
Also be carefull on what type of payments you accept. I've received several fake money orders from customers (nigerians). Always make sure the payment clears before shipping the order. Some will even send fake confirmation paypal payments to your email. Check your account and make sure the money is there.
These are just a few tips and tricks i've learned over last couple years. Goodluck and be cautious when buying.