Purchasing goods and services

A modern activity is advertising automobiles on websites. They list a (non-existent) high value car with a low price as bait to attract buyers eager to buy quickly. The scammer says "I am not in the country, but if you pay me first, a friend will drive the car around to you". The payment required may be the full price, or a deposit, but it would not be an insignificant fee. The victim never sees the car, as it does not exist. The scammers use e-mail only, as they know that the sound of their voice and their attitude will give them away as being high risk.
Another scheme involves advertising fake academic conferences and enticing academics to apply to present papers. It is a common practice that the conference subsidizes or pays for the air travel of academics who present papers at the conference, but does not pay for accommodation. One way the scammer baits the hopeful attendee is they offer free air travel to the victim, but only as long as they pre-pay for hotel accommodation. The scammer can give a variety of reasons that the accommodation must be pre-paid — primarily that they don't trust the victim will attend the conference unless he pays upfront.
Any goods or services may be used in the scam, but the idea is that the scammer baits the victim with a good deal, but the victim must pay upfront and electronically.