Amazon Marketplace Buyer using Amazon Marketplace to scam seller off on getting free merchandise Internet

I have been using Amazon Marketplace selling my merchandise for more than 10 years and I have 5 star rating service. Recently I sold a merchandise to a buyer from Amazon Marketplace, as soon as he received the merchandise just 2 business days after he placed his order with standard shipping, he falsely report to me that he didn't get his order and his order did not arrived on time so he wanted his refund only 2 business days later. The order with tracking ID clearly stated it was delivered to his address, how quickly he asked for his refund trigger a red flag of him trying to scam me already, I advise him to check his mail as well as check with his post office about the package in the evening, the next day early morning he ignored every thing I said and demanded for his refund.

He filed A-to-Z guarantee claims on me for his refund, I explained to Amazon with the order detail including tracking ID showed the package was delivery to buyer address which I can not issue refund without getting my merchandise back first and stating buyer is pulling a scam to get a free merchandise off from me, Amazon ignored my details and issued a full refund to the buyer by took away the funds from my account. Amazon did not the time into investigate this matter at all as the A-to-Z claims was honored to buyer the same day the claim was filed. Apparently any order ship without signature confirmation buyer can keep the merchandise and falsely report that his order was never received and get his money back anytime.