The first step is eschewing greed. You must be sure you are not so greedy you live on a fool's paradise.
Rather than exchanging mails on the Internet with a supposedly genuine businessman, I'll advice your heart goes after your money to find out what use it'll actually be put to. In a nutshell, visit Nigeria and carry out your own inquiries. We have genuine institutions that can help you and help us round-off con artists and save you the pains.
Always bear in mind that advertisements by Nigerian public quoted companies are not done in public placement medium of writing non-Nigerian citizens.
If you receive such a mail in your mailbox, ask for two or more clips from local Nigerian newspapers where the offer has been published and advertised.
When you find out a company's name, ask for details and visit their site.
Mind you, these sites could be misleading, check with Corporate Affairs Commission of Nigeria to find out if the company is registered to engage in genuine business in Nigeria.
Always bear in mind that it is mostly the teaming number of unemployed Nigerian youths that engage in 419- con artistry name in local parlance. They are quite daring and can produce the CBN Governor's and president's signatures to convince you and part with your money.
Always crosscheck details of your mails' contents from Nigerian con artists with the Economic And Financial Crimes Commission (EFCC) before taking a plunge.
You should be on the look out so that you do not get caught in their net; they equally operate from neighboring West African countries.
And finally, do not accept or pay for a package for anything being sent you. Instruct the person to route it to you through DHL so you'll be sure you'll not be cheated out of your hard-earned money.