Potential scam would you pay up?

I have no time to sell on eBay so I pay a guy to do it for me. I send him pictures and info and he list it then I ship. We've done this for about 10 things with no problems. I told him to list an iPhone 5 and he did so it sold for over $300. Sense then we've sold about 10 things with no issues. Now it's been about a month and half and he says the buyer opened up a case saying he never got the phone and if we can't get tracking hell get a refund.
The guy is demanding I give him $300. He says I never provided him tracking. I swear I did 110% sure I shipped. But of all receipts I can't find this one!
One thing that is making me mad he cusses me out and threatens me through text about it. I really think he is about to post my phone number on a public fourm.

what do I do? I really think hes trying to scam me he just threatens me and hasn't sent any proof theyve said anything.

He picked the one item that you canty find the receipt for, as his 'scam' target? You realize how unlikely that sounds?

You need to pay up. You never sent the item, you got caught.

Pay up, he'll go away, which solves the swearing issue.

It doesn't seem likely that he's scamming you. If he was going to scam you then I would think he'd do it on multiple items.

Just ask for a screen shot. If it's for real that will be proof.

He should not swear at you. That is very unprofessional. However, eBay will take the money out of the seller's account and refund the buyer if the seller can't prove it was delivered or at least sent. If it was sent, it is the shipper's responsibility to ask the USPS or UPS to locate it/find out what happened to it. It can't be traced from the other end.

For $300, you should have spent the extra 90 cents on tracking, if it was not included and insurance on breakable items over $150 is also a good idea. If you can't find the receipt, you need to refund your friend, because he will be out that money. Tell him you are looking for the receipt - have another look. If you can't find it within 1 week, tell him you will pay him as soon as he sends you proof that the buyer was refunded the $300. He can easily provide you proof by forwarding Paypal's notice to his email that the refund was given. Proof is also available on Paypal's website. He can copy the page showing the refund and send it to you by email.

Find a drawer or a box or something just for USPS or UPS receipts and always get tracking on costly items and insurance and tracking on breakables. You need to protect yourself. Since the buyer pays for shipping/handling, you have no excuse not to.