Here is an example, which I recently received in my mailbox, of a "deal" that I will not accept. I don't think any other legitimate writer will accept these terms, either
"I have attached my assignment and can you pplease have a look. It is 2000 word assignment and i need it by 27th December 2012. If you can provide me with 500 words to see how you go in the assignment before payment it would be great to hand pick my writer."
I am operating a business, not a charity. Payment of at least 50 percent must be made up front, meaning before the first word is written. Writers who provide "free samples" we could easily spend almost all of our time accommodating scammers.
When customers are legitimate, I find that payment arrives in my PayPal account immediately. When scammers are trying to get something for nothing to sell to their clients, there always seems to be a reason they can't pay right away.