The scam that has been running for quite some time is to over-pay with a forged cheque/document. Then ask you to pay the shipper, or wire the excess money back to them. When you do that, and then cash your cheque, it will bounce and you will be out the whole amount. Only accept cheques/documents for the actual amount. Cash it before you ship. Don't pay their shipper, etc. After about 2 weeks, when you are sure your document has properly cleared, then ship the object.
Tom