Even from high fraud countries, there are still people with integrity.
That said, talk to him. Ask about the "shady things" that occurred.
They might end up being differences that you don't understand due to your different backgrounds.
If these are not clarified, you will have doubts for a long time that could eventually wreck your relationship.
Lots of young Nigerians want to leave the country and some would do anything to get out.
So trust your gut, make a decision and live with it.
Don't make it in anger as some others have done.
Getting married is supposed to be getting a partner for life, hopefully. Not for just the next couple years.
So examine the facts and act.