You find an ad somewhere on line for a car that is just a couple of years old, low miles, good condition, facts backed up by photos and best of all, the price is really, really low.
Why so cheap? Well, the seller is just about to leave the country, or has just left the country but the car is at a port and the seller has found out that he can't ship it after all, or the seller just started working on a cruise ship and doesn't really need a car, or the seller is in the armed forces and could get sent away at any time but can't tell you when, perhaps for reasons of national security.
To pay for this car, the seller wants everything to be above board, so the idea will be to make the deal then arrange the payments through eBay. What could be more secure?
I now know three people who have been attracted by a deal like this. It is a scam. There is no car, and the buyer loses whatever deposit the seller can talk him into sending.