Since you have nothing listed on this ID and your feedback is all private, it is difficult to make useful suggestions.
Are you still selling cosmetics and what sort of price range are we talking about?
One suggestion I would NOT make is insisting on tracking.
The cost of the service usually far outweighs the value of proving delivery in the occasional instance that a claim is laid.
What would I suggest?
A)Start with deciding what countries you will ship to and which you won't.
There is a company that insures 'one-off' parcels called 'shipinsure'.
Some posters use their list of 'uninsurable' countries for this purpose, because that country has shown itself to generate an unusually high rate of insurance claims and payouts.
The company itself has a good reputation for reasonable rates and may be worth looking into.
B) Never ship by Surface.
A buyer who complains about non-delivery on a Surface shipped parcel is probably right. Surface can take months to arrive and Paypal now allows six months for Disputes.
Too slow for the price.
C) Enable a Block on bidders with Unpaid Item Strikes.
And while you are at it, look at the other possible Blocks in your Seller Preferences.
D) Tell your customer on shipping the date and service you used. I put this into the customer's Feedback.
E) Remember this is business.
The customer may even be right (see (B) above).
If you refund one payment out of 10, you do have a problem. If you lose one out of a thousand, not so much.
F) Cookie Jar Insurance.
The problem is not proving delivery. The problem is the eBay/Paypal reaction to these claims.
Don't let eBay/PP get involved.
Add a few pennies to each asking price or S&H fee and add those virtual pennies to a virtual Cookie Jar.
More sedately, you are adding a small premium to a self-insurance kitty.
If you get a claim on non-delivery, after some polite communication with the buyer, take her payment from the Cookie Jar to refund.
Enough pennies will accumulate to more than cover occasional losses.
