Ratings (by which I think you may mean feedback score) are not the same thing as NPB strikes. Non-paying bidder/buyer strikes are invisible … but powerful. Two or more over a 12 month period will see such a buyer blocked from buying from any seller who has set up their buyer requirements correctly.

Feedback score, for a buyer, bears no relation to this. Buyers can only receive positive feedback, so even a bad buyer will have 100% positive feedback. 

The strikes will not be seen by either the buyer or any seller … but the buyer will feel the effect if they find themselves unable to purchase from certain sellers.

Have you cancelled as unpaid?

Have you set your Buyer Requirements to exclude repeat non payers?

No need to send messages... eBay send reminders to pay.

eBay have no idea the 'buyer' has'nt paid and unless you/the seller cancels and uses the reason buyer did not pay do you do that?

This means you will also not have to pay those fees for the items that 'sold' that the fake buyer did not pay for

The 'buyer' would'nt need to be advised anyway, they know full well they did'nt pay

If you report the non payment, they will get a strike which will prevent them from buying from sellers who have their blocks in place

Otherwise nothing is going to 'happen' to the buyer 

And don't forget to block these 'buyers' so the same ones can't keep doing it to you