It's not just deposits, often the whole cost of the vehicle is paid up front by bank transfer. I know that seems stupid but they usually come up with a very convincing story as to why it's better for them to have the car delivered to you by courier. They do it with everything from high end camera gear to earth movers, they are making a lot of money. Camper vans seem the most popular.
If you are bored you can do some scambaiting and go as far as getting the bank details for the transfer. Once you've done that pass them on to the facebook group and they'll get the bank account frozen if they can. The same account is usually used for multiple scams as they can be hard to get setup, so when it's frozen you may actually stop them getting money they've already scammed from someone else.