I understand you are concern is regarding the A-Z claim on the account.
Now to appeal this, you would need to first understand the “Why? What? Where? Who? And How?” to get to the root cause. Once you understand the reason why this had happened, you can think about a temporary resolution and then focus on the long term precautionary steps you can take. All these three steps will build a plan of action.
Like you mentioned, sending the item through non traceable service led to the issue and I’d also like to appreciate you here for the immediate step that you had taken i.e., sending out a replacement. This shows your customer service in solving the issue. However, this is only a corrective step that you had taken but does not guarantee that this wouldn’t be repeated in the future.
Every claim will be reviewed by our A-to-z guarantee team before coming to a decision. If there is no tracking ID available, they wouldn’t be able to find out about the order status and it would be resolved in favor of the buyer and refunded.
Take a look at this page: https://sellercentral-europe.amazon.com/gp/help/G27951 to learn more about how A-to-z guarantee claim works and how you can prevent it.
Since you mentioned that the products you sell are of low value and sending them through tracked service wouldn’t be convenient for your business type, you can think about our FBA program where the packing, delivery, returns and customer services are taken care by us. Using FBA, will not impact your account with any of the issues mentioned above. Visit: https://sellercentral-europe.amazon.com/gp/help/G53921 for more information.
If you do not wish to use FBA, then you would need to think about an alternate way to ensure your buyers receive their orders on time. If you continue to use non trackable service, it may lead to valid tracking rate issues. Check this help page: https://sellercentral-europe.amazon.com/gp/help/G201817070 to know more about the valid tracking rate metric.
I hope this would help in solving the issue. You can proactive write to our team with the plan of action you have thought about to avoid review on your account. Once they receive the details, they will assist you accordingly.