Thanks Stefo and BigBri for both clarifying and qualifying what I wrote. Yes, it is the fact that the OP was being asked in advance for a substantial "gift" by an un-met "local contact" which doesn't fit the cultural piece. That's why I said I'd turn and walk away.
But I am forever fascinated by the miscommunication around this issue between Westerners and Africans. It causes no end of friction, yet both sides are often merely following the norms of their respective cultures. I'm interested in hearing you say Stefo that your husband only rarely refuses outright, which fits with my observations, yet I personally don't know how to cope with the steady requests from all directions without feeling resentful.
Hence I try to place myself in another category altogether which I don't think actually exists in indigenous terms--the outsider who is also a friend and sometimes business partner but declines to participate in this aspect of the local culture. I try to be very forthright about what I'm doing: "I know that you are accustomed to doing it this way, but where I come from this is considered a very bad idea, so I don't do it that way. Instead, I do it this way....." Results have been entirely mixed, but at least I do get to maintain my composure, unlike some.
Fortunately, Africans are not so naive about us as we are, in general terms, about them. They are also very accustomed to dealing with people from other cultures, making allowances as necessary.
Always interested in hearing more about this. I am no expert.
Mark