How much trouble?
Umm... lots, I guess!
Just for a car you often need a curious document called a "carnet de passage," basically a mechanism that prevents you from selling your vehicle inside a certain country. I assume there is something similar in place for an aircraft.
When you cross the border to anywhere, even the USA, with something you want to sell there then you need to declare that to the customs authorities. Just at a guess you probably have no experience of dealing with African customs authorities otherwise you would probably know this is a really, really stupid idea. You could easily end up with an aircraft that was impounded for forever, when you couldn't just turn around and leave ("Oh, sorry, my mistake; did I say 'sell'? I just want to fill up the tanks and be on my way back over the border, okay? Byee.") but you certainly couldn't sell this now-smuggled aircraft of yours without paying a fine that left you out of pocket.
You seem to have some notion that you can just rock up with your Cessna and slip in un-noticed, lost in the crowd. Don't let this come as a shock but in Africa many officials are grossly underpaid in terms of their offical wages; they make their money off corruption, bribery and extortion. You really want to show up with an expensive airplane to try your luck in Africa with that crowd? This would be a guaranteed attention-getter.