The illegal demanding of payment from travellers exiting Lagos is a decades-old scam. Unfortunately, they do have some leverage being in an official capacity. It is condoned higher up the chain as a portion of the proceeds must be shared w/ supervisors or they lose their jobs. It will never go away. People who do regular business there (and especially who have local representative offices) usually can get out w/o having to put up the money. The main targets are infrequent visitors, non-business transit travellers, and tourists.