Further adventures of the Duck Calmer

Here is the 'Duck Calmer' picture, which I sent a few hours ago to its prospective buyer... for £800 (because, as I said, it wasn't an antique). The buyer is offering a cheque for £1,000. He expects me to send the excess back to him. I'm posting this because it is a form of fraud and yahoo, despite promises to the contrary, are doing nothing about it. This is what he said:

"Thanks for your swift response, Further to the above, the check will get to you in the order of £1000, so once fund clear, you deduct your money and send the balance to my shipper for quick of the pick up Perharps, fund must be clear before collection, so endeavour to get back to me if it suites you with your details with which the check will be issue to effect payment."

-----------------

What next?