In this variation the scammer responds to an ad placed by a tutor-for-hire, such as a music instructor, explaining his need for a tutor for his child who will soon be relocating to the tutor’s area. Often the scammer will want a suspiciously high amount of instruction for his child and will of course want to pay for multiple weeks of instruction in advance via money order or cashier’s check. The dead give-away is usually the scammer’s request for very specific list of information e.g. « full name, address, city, state, zip, phone number » in the first or second email. The rest of the scam is the same as other fake check/wire transfer scams, where a fake check or money order for more than the agreed price is sent to the victim, then the scammer requests that the victim wire the balance back to him or someone he owes a debt.
 Escort scams
In this variant of a classified advertisement scam, a scammer answers an online escort advertisement, typically posing as a wealthy businessman traveling from Nigeria or London to the escort’s city of residence. The scammer contacts an escort claiming to be interested in a long-term companionship arrangement of days or even weeks in length, the total time involved totalling to a substantial sum of money. The scammer offers to pay in advance by cheque in excess of the net payment and asks for remittance of the balance. This version is especially popular as escorts in many cases cannot safely contact legal authorities for any reason and are unlikely to report successful or attempted fraud. A variant of the escort scam involves translators and interpreters who are asked to escort a businessman or his family for a few days.
 Rental scams
Where the victim (i.e., a prospective tenant) is looking to rent accommodation, the scammer will answer a classified advertisement offering a high-standard place for a low cost, even showing pictures of the said rooms. The victim is required to pay a deposit, but once the scammer has received the deposit he will disappear leaving the victim out-of-pocket.
Where the victim (e.g., landlord) is looking to find a tenant for their accommodation, the scammer poses as an « interested » party who is looking to move to said location. On inquiry to the prospective tenant, the victim receives a follow up e-mail indicating they will be sent a cheque by the tenant’s new employer that will cover the rent, plus the new « tenant’s » living expenses (e.g., to purchase furniture). The victim is asked to forward the additional portion to their new « tenant » by Western Union (or similar).
Where the victim posts on a communal website (e.g. Craigslist) that he/she is looking for a roommate to share a rental unit (or is a landlord looking to rent a unit), and the « scammer » poses as an interested party and sends a check to hold the room. The check will originate from overseas. The victim receives the check and desposits it into his/her bank account, and that amount of money will temporarily appear as having been added in. Within a few days the scammer then contacts the victim and advises that he/she cannot move into the rental unit due to an illness. The scammer will even provide what appears to be medical documents indicating this state of ill health. The scammer then asks the victim to immediately wire transfer the money from the check back to him/her. This takes place, and then a few days later the victim finds out from his/her bank that the original check has bounced.
Source : wikipedia