A check or money order is only a promise to pay or provide funds.
When you deposit either in your account, in essence you are making a guarantee that the funds will be provided.
There are departure taxes in certain countries (like Aruba for example), they are paid to the Customs Officials at the departure point in the airport.
A Nigerian passport holder must hold one of three visas to even land in the UK: which means individuals can "be" in the UK for up to 24 hours.
This allows them to connect to another flight within 24 hours as long as their bags are thru checked and they have been checked into their connecting flight.
An employee for an International Airline which does a huge volume in and out of Africa, via London has stated the airlines do not collect fees for anything except excess baggage, tickets or change fees.
The taxes scammers claim they have to pay do not exist.
Scammers will pose under the disguise of beautiful pictures as either male or female claiming to be from the United States.