Well i have just been bitten by e-bay and paypal. Get proof of postage it says to cover yourself for lost post - this is not the case, if you dont pay extra and get a tracking number you are up the creek without a paddle and absolutely nothing you can do to stop your buyer getting their money refunded leaving you out of pocket, in my case it is £40 plus e-bay fees plus paypal fees.
Dont make the mistake i did thinking that a proof of postage receipt is all you need to stop your customer getting their cash back if the item goes AWOL. Get that tracking number!!!