I saw this on the Marine Retailers Association Web site

There is currently a scam being run by trying to purchase previously owned boats with fraudulent cashier checks. One scenario involved an inquiry over email about a used boat seen on the website. The customer negotiates a price and requests that the seller include a quote for a shipping cost (out of state or the US). The customer sends a cashier check for more than the amount to cover any extra costs. The customer arranges for an associate to come and pick up the difference after the total is final. At the last minute, the customer calls and says that the associate is not able to come but please wire the excess funds to an account.

The seller found out that the check (apparently a computer generated item) was not legitimate and no funds were available and halted the deal before sending the product.