Before you post the item to the buyer make a note of the tracking number, as you will need to enter this later on so that it shows up against the item and automatically marks it up as having been despatched. That way if you get any allegations from the buyer to the effect that the item has not arrived you can put a trace on the tracking number and work out where the item is.
Although I gave up selling on eBay when they got rid of PayPal as the default means of sellers receiving payment for items sold I always used to buy my postage labels from the Post Office and would make a note of the tracking number for each item I was posting out, as well as ensuring that I kept the receipts of the postage labels I had bought. I would also send the buyer a quick message after the item had been posted and I had uploaded the tracking number, usually just saying something along the lines of "Thank you for your purchase. The item was posted out to you today and should be with you shortly. If you have any queries please do not hesitate to contact me."
In all the time that I sold on eBay I only ever had one Item Not Received case opened against me, which I subsequently managed to prove was false as the tracking details proved to eBay that the item had been successfully delivered to the buyer. Given that I was able to prove that the buyer had been lying I won the case and the buyer ended up finding a place on my Blocked Bidders List for trying to scam me.
