I passed this post by because I thought it was about the Nigeria emails of people asking to transfer millions to your bank account, didn't know it was something different

Anyway...
I would never send anything until a check cleared and I was sure the money was in my account (Bank, paypal or whatever).
I have been burnt before but that was when I sent payment.
I am always suspicious now but people don't mind waiting for a check to clear.
No reason for you to send them something when you have nothing for it yet.
It is like you sending something off and them saying they will send the money in a few days, after you post their item.

It is normal practise to wait for a check to clear anyway so they shouldn't mind.