You gave an example of a prophecy being given to a person that they should go to Africa. First of all, there is no way that such a prophecy could be absolutely known to be of God or not.
Paul and his co-laborers were convinced that they were supposed to go to Macedonia after Paul received a vision of a man from Macedonia in the night. His co-laborers were not the ones who saw a vision (as far as the text tells us), but they were convinced based on someone else's revelation. Churches took up collections based on Agabus' revelation about a coming famine.
Romans 12 teaches us to present our body as living sacrifices, holy and acceptable unto God that we may know what is the good, and acceptable, and perfect will of God is. We can know the will of God. The Spirit also searches the deep things of God, and Paul writes 'we have the mind of Christ.'
Timothy was to embrace prophecies spoken over him. By them he was to fight a good warfare. It is possible to discern that prophecies are genuine and then act on them.
I would encourage Christians to never follow a personal prophetic word as a directive for anything, go to the bible and pray a lot. Too many deceiving spirits out there.
There is also the Holy Spirit. I wouldn't tell Christians never to follow a personal prophetic word. I would encourage them to pray. Sometimes an individual hears a prophecy and can perceive that it is from God. Some of them just confirm what God has shown you for a long time. There are also those times where you go one place, someone prophecies something over you, and you go elsewhere and someone else prophesies the same thing. I suspect Paul had that happen when the Spirit bore witness in every city of the bonds and affliction that awaited him.
I remember the story of a single young man who traveled around to various churches holding meetings and in every church some single woman would tell him, that God wanted him to marry her(sometimes there was more then one). It is just too easy for us to think that God told us something when He did not.
We shouldn't believe every prophecy. I know a man who was a widower, an evangelist, who was praying for a wife. A single Russian woman who was very active in one of the churches he planted was at a conference for the churches where he was speaking, and believed God told her they were to get married. She told her mother. Eventually, it got back to him and he was all for it. I never really heard his description of his prayer and thought process. They are in a different country, so that may not happen.
I didn't know this at the time, but my wife told me that before we had our first conversation (we'd actually been introduced before and figured that out later), that the Lord had told her that I was the one for her. I went home and prayed and asked God if this was the woman I was supposed to marry. I can't say I heard God say that the first day, though that came later. But a little while into the relationship, and I'd thought He might have been telling me I'd meet her that month. But I was wondering if that was just me at the time. There are plenty of testimonies from people who can tell you the Lord told them who they were to marry beforehand.
There does need to be more teaching in some of these churches against prophesying falsely in the name of the Lord, too.
