shipping scams

A common online scam is the shipping or money order scam.

This is what typically happens:

The scammer contacts you with the pretense that they are interested in something you are selling online. This is usually something oversized and/or requiring special shipping attention (e.g. cars, livestock, oversized artwork).
The scammer moves very quickly to the details regarding payment and shipment.
They will always tell you that they will have someone get the item from you directly or that they have a specific shipper with whom they always do business. They will inform you that they will send you a cheque/money order for the cost of the item they are buying plus the cost of shipping and ask you to pay the shipper after you cash the cheque. This should usually be your first warning that the buyer is actually a scammer. If you suggest a different shipper, you probably will not hear from them again.
If you decide to play along or are unaware of the fact that this is a scam, they will ask for your address so that they can send you the cheque/money order. They may also ask for your phone number so they can call you if you do not cash the cheque and send them theirs quickly.
While you wait for the payment, you will probably be contacted several times via email with a request to confirm whether you have received the payment. Often, they send the cheque/money order through a method with tracking so they know when you sign for it.
Once you receive the payment, they will urge you to cash as quickly as possible. Luckily, the scam has been around enough that most financial institutions are aware of it and know to validate cheques/money orders which are suspect. Reportedly, the cheques usually look and feel very real.
They will then ask you to use Western Union to send money to your shipper. This email will be quite long and detailed. The email will include a name and an address of the supposed shipper (usually a fake one; no ID with an address is required to accept the transfer), and a request for your test question & answer, control number, amount sent and your name and address (again). Often, they will even provide you with a list of Western Unions in your area.
If you are still unaware that this is a scam and go through with all of that, you will have lost much money. If you're lucky, the financial institutions with which you do business will have noticed something odd in the cheque you tried to cash. Because the scammers have now stopped providing addresses in Nigeria (where most of them operate), it is difficult for Western Union to know when you are being asked to send money to a scammer. What would happen now is that they get your real money and you are left with a bogus cheque which will be discovered a few days later. In many unfortunate cases, the persons who have been scammed are in debt as a result of the scam.

How to identify the scam:

Awkward English (e.g. strange choices of words, incorrect punctuation, careless spacing between words and punctuation).
The "buyer" is in a hurry to close the deal and does not request much information regarding what they are buying.
The "buyer" uses a private shipper.

How to protect yourself against this scam without alienating a potential client:

Insist on a contract or letter of agreement for the transaction. In the case of a real transaction, this would protect both your interests and the interests of your buyer. Deal with them professionally. If you are dealing with a scammer, they will either stop contacting you immediately or try to dissuade or delay you from a contract. Someone who is a real art buyer will feel more comfortable with this type of professionalism. If the work has not yet been created, you would want to insist on a contract and a deposit to cover the costs of materials.
Suggest a different shipper and/or ask for the name of their shipper. It is possible that a real art buyer would have their own shipper if they are a frequent buyer, but you would be able to find the shipper through an official phone directory. If you are dealing with a real art buyer, they should at least be receptive to the suggestion of a different shipper (artists, too, have a preferred shipper), especially if they can be sent the artwork with the same security for less money. If you are dealing with a scammer, they'll probably decide that you're too much trouble and stop responding.
Ask yourself, honestly, whether the sale sounds too good to be true. In Rick's case, the scammer claimed to have been referred by a friend and Rick had been completing many sales in that time, so the sale seemed legitimate. However, in my case, all of my sales had been made through shows or existing patrons and I'm a relatively unknown artist. Don't let your ego or your hope for "discovery" lead you into debt!

Real examples of the scam: