Then hang on to your shit, be patient and wait till someone who seems a bit more legit comes by.
What are you selling exactly?
Since hes going through paypal he not sending you the usual "Ill send you $2000, you send me back the remaining $1200 from that" type of shit?
Personally, not to sound like an ass, I wouldnt go through with it, however I dont know the details of your transaction so thats taking a very blinded pov. Thats not to say people in Nigeria arent legit and the fact that a lot of scams come from that region of the world is unfortunate, but like a lot of things it only takes the few bad apples to taint the rest.
If you want the peace of mind that you wont get fucked. Stay closer to yourself.
If its not mega sketchy and you feel comfortable, then move ahead.
As far as customs and stuff, depending on your claim value that you list and also the type of shipping you choose you may or may not be covering duty.