There are 2 ways they can scam you.
1) They send a fake email looking as if its from paypal. This will say you have received a payment and have link to click on. This will be the start of your problems. DO NOT OPEN THE LINK. Always type the address yourself or saved in bookmarks.
2) This method is usually used when you are looking to buy a car, but could easily have the roles reversed. They will send you a document from the "shipping company" to say they have the car and asking for payment to be made to them. They say will deliver the car for you to inspect and only release your payment to the seller when you are happy. However, THE SHIPPING COMPANY IS FAKE, IT DOES NOT EXIST. Never send any money, you will never see the car.
When the scammers put ads on auto trader they used to always be low mileage cars with top spec for a ridiculous price. Maybe 8k for a car worth 20k. However, probably due to more people becoming aware, they have changed slightly. The same car they will now advertise for about 15k to make it more believable.
They also put a phone number which does not exist so you are forced to email them. Lately they have been using email addresses which make it look as if they are a trader or set up a simple web page with a link for the same effect. Basically as it becomes harder for them to scam, they are trying harder to make you believe its a genuine ad. Always be wary of a car that looks very cheap. Always try to see the car in person and don't take cash with you on first visit.
And Merry Xmas to all