The military leave scam occurs when the "soldier" you are in contact with mentions that he wants to visit you, and just needs to file for military leave. You will be required to do certain things, including talking to a "superior officer" who is either the scammer himself or an accomplice. The scammer will ask for certain information, and then will send you falsified documentation, and a number of forms, which you will be asked to fill out and return. You will also likely be asked to pay a "replacement officer fee". You will be told that the payment can be received via Western Union or Money Gram. There are scammers that do have bank accounts for this kind of scamming.
This scam begins with the scammer telling you that he is going to be sent to an area without regular phone service, internet, or otherwise. He asks that you send a special phone that will help you be able to stay in contact with him. He will say that it is the only way he knows to maintain contact. The scammer will try to send you to a "company representative" who is in league with the scammer or the scammer himself, or you may be sent to a website that appears legitimate, where you fill out personal details. At some point he will ask you to pay for the satellite phone service, telling you that he will return the money quickly.
A package is "shipped" to a woman from a man she met online. He says that he will not be able to send you the package unless a fine is paid, roughly 300-700 dollars.
The scammer will say that his money order that he received from his boss cannot be cashed where he is. He sends out the money order to the victim, and tells her to add it to her account. In the mean time, while this money order is coming, he wants her to enter money into his account using Western Union. When the victim receives the money order, it is useless. Be very careful with handling this money order - attempting to cash it may lead to banks to filing suit against you.
The scammer will usually spot a victim on a dating website and get in contact with her. Soon, the victim will receive notices from governments in Africa, notably Nigeria, saying that the boyfriend of the victim has a large amount of money in diamonds and gold, as well as other cash that requires laundering, and if that money can be sent to the victims country using the victims account information, than the victim can share in some of the profits. The victim sends out the information, with the promise that the money will be coming soon. In the mean time, the false government officials ask for money required to perform certain acts, such as bribing officials, paying taxes, and paying off legal fees. These fines are promised to be returned to the victim. However, the truth is the millions in gold and diamonds was never real at all, and even after the victim stops sending out money to the scammers, they will use the victims account information for identity theft. While this kind of scam is sure to set off warning signs from the beginning, many victims have fallen for such a thing, and some have even gone to Nigeria and been imprisoned for ransom.
This kind of scam occurs over time while the scammer builds up trust with the victim. The scammer is not simply sending general letters - he is sending personal messages and seems to provide the victim with a false sense of security that he loves her. This goes on for some time, until the first part of the scam begins. The scammer asks for monetary help with obtaining a visa, plane ticket, and insurance. At this point, once money has exchanged hands, the scammer will usually depart and never be heard from again. Other scammers will continue with the love affair, giving his victim a number of updates about his travels. Soon he will run out of money, and he needs to be sent more. Maybe he is robbed, maybe his plane ticket shot up in price. In any case, as long as the victim continues to give money to the scammer, the scammer will not stop. Once money stops coming, the scammer disappears.
This kind of scam is one of the most common to occur. Much like the Travel scenario, the scammer builds up a connection with the victim. He continues until he feels the victim is ready for the scam: he says that a relative is direly ill, and that it appears that the person will die unless he/she gets aid soon. He turns to the victim, hoping that she will help him fund the hospital bills. When the victim stops sending money, the scammer disappears.
This scam is a conglomeration of all of them really: scammers will find a create way to tell the victim that they are in serious trouble without money. They may say that they are waiting for a check to clear, that they have business problems, that they were robbed, or that their bank accounts were frozen for unjust reasons, his credit card is not accepted where he is, and a million other things ranging from medical expenses to food to hotels.
The scammer will perform the same acts as above, but uses a dating website that caters to gay men.