It is said by those who know first hand that more than a few folks do a single rotation into Nigeria before doing a runner for other places. That would indicate the home office knows of the magnitude of the problem in manning Nigeria.
The most important thing to remember in dealing with prospective employers is to be completely honest and up front with them. Ask the hard questions of them and evaluate their responses. If they become evasive, unclear, and either get uneasy or hostile....be careful in accepting that offer.
Interviews should be a two way street.....feel free to ask questions of them. The decision to hire on someplace is just as important as deciding upon marriage as hopefully it will be a life time affair.