I do not know how the drivers kept some of these vehicles running, especially given the bad conditions of the roads. On the other hand, we also did see a lot of broken down vehicles, many in the process of getting fixed by the road-side as the passengers patiently waited.
As a side note, Guinee's public transit system is practically non-existent. I only saw a few buses, and those were only running out of Conakry, There is one railway line that appears to have been recently renovated. The people in the country depend on bush-taxis to get around, regardless of the distance that needs to be covered.
The PCVs are used to traveling between towns in such bush taxis stuffed with people. In addition to goods, animals and people are also carried on the roofs of these vehicles.