I thought everyone knew about it... here is how it works. Someone contacts you about your art or dog or furniture whatever. Says he'll pay with a certified cashiers check only. After the sale you get a check in the mail for thousands over the amount. You contact him he tells you to just cash it and take what you were owed and mail the rest in a check to him (usually thousands over the original amount) and sometimes they tell you to keep an extra couple hundred for the inconvenience. You do this and in a couple weeks when the bank finds out it was a counterfit check... then you owe the full amount of it even though you had no idea.
I assumed everyone knew about this scam already. Anway... there are various forms of it and with artists they like to even list some of your art to make it seem more legit. For anything other than local sales I only accept credit card or pay pal.