Don't be so hasty, they are not ALL doctors, I have recieved some from barristers, as well as high ranking government officials.
For those that can't exactly figure how the scam works, it's not your car/parts/motorcycle they want it is your $'s. That's why the "shipping" cost are included, they rely on people to quickly return the "shipping" cost to expedite the deal, and then when their counterfeit check/money order comes back you are screwed. Also,I agree with the comment about giving your bank #'s out, they could also suck your funds out before you are aware of it and the banks usually don't want to take any responsibility for transferring your funds away.