Much like the other scams detailed here this involves the promise of an item when all the necessary fees have been advanced. Adverts are taken out by someone who is claiming they are the breeder of puppies they sold and they are not doing well in their current situation. The owner claims to be looking for someone to adopt them back. They also claim to work as a missionary or for the United Nations. The advance fees in this case being for the purchase of the animal and ‘customs’ charges that will never end.
In these scams, the scammer will pose as a terminally ill mother, poor college student, or other down-on-their-luck person and ask for money for college tuition, to sponsor their children, or a similar ruse. The money, they say, will be repaid plus interest by some third party at a later date (most of these third parties are some fictitious agency of the Nigerian government). These can be amongst the most insidious scams because they target charitable people who believe they are actually helping someone to get back on their feet or look after their kids and do not necessarily expect a payoff at the end (though usually one is offered). Once the victim starts paying money to the scammer, the scammer will tell the victim that additional money is needed for unforeseen expenses, similar to the “puppy” scam above; In the case of the ill mother, the children will fall ill as well and require money for a doctor’s care and medicine, where the student might claim that a dormitory fire destroyed everything they own. These calamities, and the requests for ever-larger sums of money, will never end, similar to most other variants of 419 fraud.
Source : wikipedia