Credit card use through IP Relay
In another variation of the scam, the scammer places calls through IP Relay, a US federally funded internet telerelay service for deaf/hard of hearing/speech-disabled individuals. The scammer calls various businesses, attempting to purchase items with stolen or fraudulent credit cards. Often, individuals are targeted as well, most of whom have advertised a product or service online. 
Typically, in an IP-Relay scam call, the scammer will place several calls using a Relay Operator. Calling to businesses or private parties, the scammer will inquire about merchandise/services offered, and then immediately and with few questions asked, attempt to purchase the merchandise. The scammer (who refer to each other as « guyman ») then proceeds to ask the potential victim (known in Nigeria as a « Mugu »; a Lagos pidgin word for « fool ») for an e-mail address, by which he can contact the victim to proceed with the closing of the fraudulent transaction.
The scammer proceeds to send the victim a counterfeit cheque or money order, with instructions requiring that it be cashed, and that excess funds be sent back to the scammer (advance fee fraud). When it is determined by the authorities that the money order is counterfeit, the victim is usually arrested and charged with various offenses relating to the scam.
Credit-card fraud is not the only kind of fraud reported through IP Relay. A relay scammer typically will use IP Relay for all fraudulent-related transactions/telephone calls within the United States.
Often a scammer will browse through online classified ads (such as craigslist.org) and will use the IP Relay service to contact sellers to make inquiries about the item listed in the ad. Most commonly the scammers target persons whose ads advertise live animals (i.e. puppies), automobiles, high-dollar electronic devices, etc. In this scenario, the scammer sends the seller a cheque for the advertised item with an overpayment. The victim is given instructions to cash the cheque or money-order and to wire the remaining balance via Western Union or Moneygram. The victim is at a loss in this situation when the authorities discover the cheque/money order is not legitimate.
Because of current FCC regulations and confidentiality laws, operators are required to relay every call verbatim and must adhere to a strict code of confidentiality and ethics. Thus no relay operator is permitted to make judgements about the legality and/or legitimacy of any relay call and must relay the call without interference. As such, the relay operator cannot warn victims even when they suspect that the call is a scam; Some sources claim that up to half of all IP relay calls are scams.
Some IP Relay companies have certain fraud criteria in which a supervisor is able to come on the line and inform the person that has been called that the call « fits a pattern of fraudulent and illegal activity ». It is then up to the voice person whether he or she wishes to continue the call.
There is a ring with a Ft Lauderdale phone number area code (954) who attempt to purchase large amounts of blood glucose meters using this scam to con unsuspecting retail pharmacies. They try to send DHL to pick up the packages (prepaid shipping) to be sent to Nigeria.
Source : wikipedia