Here ya go. This is a text book scam,
Your payment has been sent but there is something i think i must bring to your notice. I just found out that my Assistant overpaid you. The payment meant for another item was made out in your name and sent to you. However I want to believe I wont have a problem with you on this. Once you receive the payment, Please proceed to the bank and cash the payment, deduct your money and send back the Balance to me through western union/money gram. So I can proceed with arrangement for pick-up. Once more, I hope I can fully trust you with this? I will await your response on this so my mind can be at ease.