Traders gone missing in the mail

How would you deal in a situation like you send your trade stuff in good faith and it gets lost in the mail? It happened to me once and it happened on my first trade and after a few months I had to send the same item again. How do I know that I wasn't scammed into sending 2 sets to that person? I just heard from other collectors that he was trustworthy. But what if you didn't know the person too well? What would you do? do you tell him that you sent it in the mail and it's out of your control when it gets lost and show him a copy of the postal receipt? Or, you send a replacement?

Your thoughts...

Track and insure everything . or just send another set or send their stuff back , and depending on who it is , I sometimes will not trade again , some countries are worse then others for losing packages .
Sometimes I just take the loss ...