The only reason a buyer would not have buyer protection is multiple sellers have reported them for scamming. eBay will then remove them from the buyer protection program. I have no idea what equation eBay uses to determine whether to remove a buyer. Based on what I've seen, I would guess that accounts that are newer and have more reports in a short period of time are more likely to be removed. I have seen some buyers who based on their feedback consistently have problems with sellers on a regular basis, and they are not removed. My guess would be because their accounts are 5+ years old, it takes more for them to get nerfed by eBay.
If you sent via Canada Post Lettermail, it isn't out of the ordinary for a package to take 3-4 weeks, sometimes longer. The thing you have to understand about Lettermail is that it isn't consistent like Expedited. Usually, if I send something within my own city it will take 2-3 days to get delivered. That doesn't mean it cannot end up taking 2-4 weeks in a worst case scenario.
Additionally, if it is going to BC, there is a much greater chance this is a genuine delay. BC has had some issues with delays over the last few months. I think I received more INRs or inquiries about late packages from BC in the last 2 months than I have received in the last 3 or so years. (Still a small number)
In my experience, most lettermail INRs are due to delayed packages. I know this, because more often than not a buyer will close the INR when it arrives, or they will contact me to pay back the refund when it arrives. While most INRs are genuine delayed packages, there are rare cases where I look at the buyer's feedback profile, and it's obvious they are a scammer. It does happen, but it's not common. It also isn't as common with new accounts. Usually, new accounts don't know how eBay buyer protection works and do not know that they can abuse the system to get a refund for an untracked item.
If your listings have Canada Post Lettermail as the shipping method, you should consider changing it to Economy Shipping. eBay's Lettermail shipping estimate is not realistic since it is based Canada Post's lettermail estimate, which is not guaranteed, and therefore not always accurate. Changing to the generic Economy Shipping method gives a more accurate shipping window to the buyer. Some buyers don't understand that with an untracked item, the expected delivery date is an estimate. If the item doesn't arrive by this date, they assume something is wrong and that it is lost. Which is why advertising a shipping method with a longer delivery window helps stop INRs. Your item arrives before the expected delivery date.
Let the buyer know that their package was already sent, and apologize for Canada Post not delivering it before the estimated delivery date. If they haven't opened an INR case, I would politely ask them if they could wait a little bit longer before doing so because it is very likely to arrive. If they open an INR, refund by the deadline, and politely request that they either refuse the package when it arrives or message you to pay back the refund.
Once an INR is opened for an untracked item, you should refund before the deadline. If you don't, eBay will refund the item, and you will get a defect. Refunding yourself increases the odds that a customer if they are genuine will pay you back when the item arrives. It also keeps your account defect free.
INRs almost never happen if your listings are set up properly to give the customer a fair shipping estimate, and if you communicate with the customer when your item is sent. Ignoring the increase from BC, the average I'd say is lower than 1 percent. Maybe close to half a percent. Of course, this is category dependent. Some categories might have a higher rate of fraud than others, which will raise the INR rate.
