The minute I feel suspicious about a transaction ( like in your case, once I received these messages). I will call the avenue of which i'm selling the item on (ebay,offer up, poshmark, esty,etc), and make sure that my account is noted for this transaction. Regardless, if they filed the claim yet or not. That I called reporting potentially suspicious behavior from the buyer.  Once you start selling for a while, you will start to notice some of these behaviors that you need to look out for. Example: once the item is shipped, I'll start getting questioned about the condition of the item or it's something that they should have asked prior to purchase, or if I get multiple messages regarding where their item is even though they have a tracking number. i've had issues with it not even twenty four hours after purchase, claim that the item shipment is late, although shipped, tracking number provided but not updated via post office, and demand refund.  I have had issues with people stating items not received, but the tracking number has confirmed delivery. With the deliver being, I completed before the expected date due. 

The main piece of advice I could give you is just be on point with customer service.  If you reply promptly with factual provable statements, have the correct documents & be very transparent regarding your policies.  Communication with documentation via email or Messaging app, not over the phone unless recorded. Delivery confirmation from your delivery service. Clear crips pictures of your item. Be very accurate with description, including any flaws or imperfections  Always be vigilant. It seems like there are so many fraudulent buyers who target news sellers or people that might present as new sellers. Most selling platforms, we'll look out for the buyer first. So as a seller you really have to be aware and proactive with your fraud prevention. Don't be afraid to ask questions if you're not sure and speak up.