How to block known scam buyers

It is common knowledge - it is even discussed widely in groups on places like facebook - that a customer can order a product and then claim non-delivery after it has been received, at which point amazon will almost always give them a refund. Hell, you can even find people in facebook groups advising other folks to do it if they want cheap products.

Our products are made to order and have a limited shelf life of 7-10 days and are totally inappropriate for FBA so we ship via Royal Mail Tracked 24. I've had a dodgy claim today for non delivery (photo of delivery provided by RM).

I understand that amazon will just refund any {moderator edit :Sakura, insult} that tries this and kinda accept that, but sellers MUST be able to block orders from known scammers and yet all I can see online is that despite being expected to comply with every law relating to online sales, sellers are also expected to support thieves by sending them free goods. From what I read, if I cancel an order, it counts against a seller. That is totally insane - no different than being forced by law to allow known shoplifters to enter a store despite the legal right (in the UK) to choose NOT to sell or to deny access to any person or persons.

How can this be in any way fair, ethical or even logical?

Please correct me if my reading is wrong and I can indeed block such scam artists.